Chapter 1 - Language, Homeostatis And Structrual Organization Flashcards
Anatomical position
Standing erect, face forward, upper limbs at the side, feet together, palms facing anteriorly with thumbs away from the body
Frontal plane
Also called coronal, divides the body into anterior and posterior parts
Transverse plane
Also called horizontal, divides the body into superior and inferior parts
Sagittal plane
Splits the body into right and left
Oblique plane
When a cut is made along an axis other than a right angle cut
Anterior
At or near the front of the body
Posterior
At or near the back of the body
Midline
An imaginary vertical line that divides the body equally (right down the middle)
Lateral
Father from the midline
Medial
Nearer the midline
Superior
Towards the head / upper part of a structure
Inferior
Away from the head / lower part of a structure
Superficial
Close to the surface of the body
Deep
Away from the surface of the body
Body cavities
Any fluid-filled space, space where the organs develop, most cavities provide room for the organs to adjust and contains protective membranes and sometimes bones that protect the organs
Name the body cavities?
Cranial, vertebral, thoracic (containing the pericardial and pleural cavity), abdominal and pelvic cavity
What is in the cranial cavity
Space occupied by the brain, enclosed by the cranium
What is in the spinal cavity
Space occupied by the spinal cord enclosed by the vertebral column making up the backbone. Spinal cavity is continuous with the cranial cavity
What is in the thoracic cavity
Space occupied by the ventral internal organs superior to the diaphragm, including lungs, trachea, and the heart, surrounded by the ribs and the chest wall muscles
Contains the pleural cavity (lateral) - holds the lungs and,
Mediastinum (medial) - pericardial cavity that holds the heart, esophagus and trachea
What is in the abdominopelvic cavity
The abdominal cavity and will of the digestive organs and the pelvic cavity with the bladder and reproductive organ
What is in the abdominal cavity
Ventral internal organs inferior to the diaphragm and superior to the pelvic girdle, cavity surrounded by the abdominal wall and the pelvic girdle
What is found in the dorsal body cavity
Cranial and vertebral cavities, contains and protects the brain and spinal cord
What is found in the ventral body cavity
Thoracic cavity, abdominopelvic cavity, abdominal cavity, pelvic cavity and peritoneal cavity
What is found in the pelvic cavity
Inferior portion (compared to abdominal cavity), found in the bony pelvis, contains the reproductive organs and bladder
Serous cavities
Small space between two serous membranes (a thin double layered membrane), serous fluid is found within this small space. The part of the membrane that is lining the cavity walls is known as the parietal serosa and it folds over onto itself to make the visceral serosa which covers the organs in the cavity
3 different serous cavities
Pericardial cavity, pleural cavity and peritoneal cavity
Pericardial cavity
The space between the two layers of the pericardium that surrounds the heart. The pericardium is a double walled sac that holds the heart and the roots to the great vessels - holds the heart in place and provides a barrier to infection. The space is filled with pericardial fluid. Made up of outer fibrous pericardium and the inner serous pericardium
What makes up the inner serous pericardium
Parietal pericardium is attached to the fibrous (outer) pericardium and the visceral pericardium / epicardium is on the surface of the heart
What is the pleural cavity
The pleural cavity is a fluid-filled space that surrounds the lungs. It is found in the thorax, separating the lungs from its surrounding structures. The pleural cavity is bounded by a double layered serous membrane called pleura. The pleura is formed by an inner visceral pleura and an outer parietal layer. Between these layers is the pleural cavity that contains serous fluid which helps to lubricate the cavity and allows the lungs to move freely during breathing
What is the peritoneal cavity
It is the largest serous membrane in the body (surface area about the same as the skin). It is made up of two continuous layers including the parietal peritoneum that has contact with and loosely attaches to the abdominal wall and the visceral peritoneum which covers the viscera (the abdominal organs of digestion - stomach, intestines, etc..). Serous fluid fills the peritoneal cavity between these two layers
Ascites
A condition in which fluid collects in spaces within your abdomen. If severe, ascites may be painful. It can set the stage for an infection in your abdomen and the fluid may also move into your chest and surround your lungs. Most common cause of ascites is cirrhosis of the liver or different types of cancer
What are the 9 regions of the abdomen? (Right to left, top to bottom)
Right hypochondriac region, epigastric region, left hypochondria region, right lumbar region, umbilical region, left lumbar region, right iliac (inguinal) region, hypogastric region and left iliac (inguinal) region
What is found in the right hypochondriac region
Liver, gall bladder, the right kidney and parts of the small intestine
What is found in the epigastric region
Liver, part of the stomach, duodenum and pancreas, part of the spleen and adrenal glands
What is found in the left hypochondriac region
Contains part of the spleen, the left kidney, part of the stomach, the pancreas and parts of the colon
What is found in the right lumbar region
Gall bladder, right kidney, part of the liver and ascending colon
What is found in the left lumbar region
The descending colon, left kidney and part of the spleen
What is found in the umbilical region
The umbilicus, many parts of the intestines (duodenum, jejunum and the ileum), contains transverse colon and bottom portions of the left and right kidneys
What is found in the right iliac region
Contains the appendix, the cecum and the right iliac fossa (pain here often associated with appendicitis)
What is found in the left iliac region
Descending colon, sigmoid colon and the left iliac fossa
What is found in the hypogastric region
Contains the organs around the pubic bone - the bladder, part of the sigmoid colon, the anus and many organs of the reproductive system
Chemical level of organization
The simplest level of hierarchy, building blocks of all matter (atoms), combine to form molecules
Tissue level of organization
Tissue is made up of groups of cells that carry out a similar function. The four basic types are - epithelium, muscle, connective tissue and nervous tissue
Organ level of organization
Made up of at least 2 types of tissue to serve a function within the body
3 major parts of the human cell
Plasma membrane, cytoplasm and nucleus
Plasma membrane
Made up of primarily proteins in a phospholipid bilateral - made of polar hydrophilic (heads) and non-polar hydrophobic (tails) built from fatty acid chains. Hydrophilic heads are attached to water (found on outside extracellular and inside intracellular fluid, faces outside and inside surfaces of the membrane). Hydrophobic tails avoid water and are found in between the two layers of the membrane
Ability of the plasma membrane
The priorities of the heads and tails of the plasma membrane means it will easily assemble together to form a spherical structure and when torn it will reveal themselves. The membrane is a fluid structure which is always in flux
Proteins found within the cell membrane
Integral proteins - found within the bilateral, used mostly for transport
Peripheral proteins - loosely attached to integral proteins, mostly enzymes or support for the membrane
Glycoprotein
Protein with carbohydrate attached
Glycolipid
Lipid with carbohydrate attached
Functions of the cell membrane
Transport - hydrophilic channels allow water to pass (couldn’t with hydrophobic tails), active pumps to move substance across membranes
Signal transduction - the movement of a “message” from outside of the cell to the inside, allowing the cell to perform the correct response
Provides attachment for other cells or extracellular matrix
Passive transport
Molecules moving with a concentration gradient, no energy required
Diffusion
Molecules move from high concentration to low concentration to achieve equilibrium. To move through membrane “it” has to be - lipid soluble, small enough to pass through channels or be assisted by a carrier protein
Speed of diffusion
Dependent on the kinetic energy of the molecules
Simple diffusion
Unassisted, for small, hydrophobic, non-polar, lipid soluble molecules
Osmosis
The spontaneous diffusion of water or other solvent through a semi-permeable membrane down its concentration gradient, moves to dilute the more concentrated solution
Solute
Something that is found dissolved in the solvent (ex. Salt (NA) in water)
Facilitated diffusion
The movement of certain molecules using a passive transport method to pass through the bilateral, done using proteins which act as carriers in the membrane (carrier-facilitated diffusion) or using water-filled protein channels (channel-mediated facilitated diffusion)
Osmolarity
The number of particles (ions) per litre of solution, only concerned with the number of particles, not size or composition
Isotonic solution
Same osmolarity as body fluids, no movement
Hypotonic solution
Hypotonic solution has a lower concentration of solutes than the cell, due to osmotic pressure, water will then diffuse into the cell to even out and the cell will appear turgid (or bloated)
Hypertonic solution
The solution contains more dissolved particles than the cell, therefore water will leave the cell to dilute the fluid around it, this causes the cell to look shrivelled
Active transport
Requires energy to move molecules against their concentration gradient
Sodium-Potassium pump
Sodium in cytoplasm of cell binds to the Na/K pump, this binding causes the breakdown of ATP into ADP and Pi, this phosphorylation process causes the receptor to change shape and release sodium out of the cell.
Potassium then binds from the extracellular fluid and causes the release of the phosphate group which causes the original shape of the receptor to be returned and potassium is released into the cytoplasm (the intracellular space)
Homeostasis
Maintaining internal conditions despite changes in the environment - balancing act, requiring endocrine and nervous system to maintain
Homeostatic regulation
Adjustments in physiological systems that preserve homeostasis
Negative feedback loop
3 main components - receptor, control centre and effector
- stimulus produces change in variable which is detected by the receptor
- this information is sent along afferent pathway to control centre
- control centre puts out information along efferent pathway to effector
- response of effector feeds back to reduce the effect of the stimulus and returns variable to homeostatic level
Positive feedback loop
The initial stimulus produces a response in the body to enhance the original condition of the stimulus thus increasing it
- body wants to keep adding to the situation which caused the stimulus in the first place
Example of positive feedback loop
Oxytocin is released by stimulation of stretch receptors during labour and this intensifies the contractions to become more powerful and frequent and these contractions produce more oxytocin to continue cycle when delivery
Example of negative feedback loop
Reduction in body temperature below homeostatic level results in hypothalamus sending message to shiver and this muscle contractions release heat to raise temperature, once reach, initial stimulus shuts off
Beginning process of metabolic process, simple terms
Carbohydrates, fats and proteins consumed, broken down into absorbable forms - amino acids, glycerol and fatty acids and glucose (or other sugars), these are then transported through the blood to tissues
Anabolism
Incorporation into molecules - using building blocks to form larger molecules (ex. Amino acids into proteins and glycerol and fatty acids into triglycerides)
Catabolism
Breakdown of larger molecules into smaller ones (component parts)
Aerobic respiration
With oxygen, 3 stages - glycolysis, Krebs cycle (citric acid cycle) and oxidative phosphorylation
Anaerobic respiration
Sufficient oxygen not prescient, energy from glycolysis
Steps of glycolysis
- Glucose (6 carbons) converted into glucose 6 phosphate by hexokinase, ATP to ADP
- glucose 6-phosphate rearranged into fructose 6 phosphate by phosphoglucose isomerase
- fructose 6-phosphate converted into fructose 1-6 biphosphate by phosphofructose kinase, ATP into ADP
- fructose 1-6 biphosphate broken down into DHAP (dihydroxyacetone phosphate) and glyceraldehyde 3-phosphate
- DHAP converted into glyceraldehyde 3-phosphate (now 2)
- both glyceraldehyde 3-phosphate each go through following steps
- G3P converted into 1,3 bisphosphoglycerate, NAD —> NADH + H
- 1,3 biphosphoglycerate converted into 3-phosphoglycerate, ADP —> ATP
- 3-phosphoglycerate into 2-phosphoglycerate
- 2-phosphoglycerate into PEP, water released
- PEP into pyruvate, ADP into ATP
Glycolysis products
2 ATP (net), 4 total, 2 NADH and 2 pyruvate molecules
Advantages of aerobic metabolism
With oxygen is much better at producing energy (ATP) and produces less harmful byproducts (CO2)
- 30-32 ATP produced in the best conditions, compared to anaerobic which produces 2 ATP per cycle
Disadvantage of anaerobic respiration
Lactic acid and more CO2 produced, harmful byproducts
In the absence of oxygen, pyruvate ..
Gets rerouted into fermentation to get lactic acid
With sufficient oxygen, pyruvate …
Pyruvate moves into the inner mitochondrial membrane, then moves into Krebs cycle (citric acid cycle and then ultimately oxidative phosphorylation)
Krebs cycle
- pyruvate oxidized into acetyl-coA (NAD—> NADH)
- acetyl-coA into citrate into isocitrate
- isocitrate converted into alpha-ketoglutarate (NAD—> NADH, CO2 released)
- alpha-ketoglutarate into succinyl coA (NAD—> NADH, CO2 released)
- succinyl coA into succinate (GDP—>GTP, ADP—>ATP)
- succinate into fumarate (FAD—>FADH2)
- fumarate into malate (water added)
- malate into oxaloacetate (NAD—>NADH)
- oxaloacetate oxidized into acetyl-coA to begin cycle again
Products of kreb’s cycle
Per pyruvic acid = 2 CO2, 4 reduced enzymes (3 NADH, 1 FADH2) and 1 ATP
2 pyruvic acids from 1 glucose (x2 for total glycolysis to kreb’s cycle)
Oxidative phosphorylation
- Reduced co-enzymes (FADH2 and NADH) deliver electrons picked up during the last few phases to complexes I and II
- electrons transferred from one complex to another down the membrane
- each complex is reduced and then oxidized releasing energy that is used to pump H+ into the inter membrane space which creates an electrochemical gradient between the matrix and the inter membrane space
- coenzyme Q (ubiquinone) and cytochrome C are mobile carriers that shuttle between the larger complexes
- at complex IV, electron pairs combine with two protons to form water
- at complex V, called ATP synthase, energy from the proton gradient allows the synthesis of ADP into ATP
- produces about 24-28 ATP
Lactic acid cycle - presence of oxygen
Lactate gets oxidized back to pyruvate and sent to the aerobic pathway.
Lactate is taken over to the liver and is converted back to sugar via gluconeogenesis known as the lactic acid cycle or the cori cycle
- if this new glucose is not currently needed it can be stored as glycogen (using glycogenesis)
Lactate in the absence of oxygen
Lactate will continue to build up, when lactic acid is produced it immediately dissociates into lactate and hydrogen ion (proton) which increases the acidity of the cell (drops pH) and contributes to fatigue of the muscle and reduced firing strength
Gluconeogenesis in the liver (simple terms)
Lactate converted back to pyruvate and 6 ATP are needed to reform glucose
Glycogenesis
Glucose molecules are combined into long chains of glycogen to then be stored for later use
Excess glucose
Majority of it will be stored as fat (about 80-85% of energy storage is in the form of fat)
Glycogenolysis
Glycogen broken down, glycogen converted into glucose 1-phosphate and then glucose 6-phosphate
- glucose 6-phosphate is trapped in the cell because it cannot cross the membrane
- hepatocytes (and some kidney and intestinal cells) contain glucose 6-phosphate (G6P) to produce free glucose (now can leave the cell and enter the blood stream)
- large glycogen storage in liver
Glucagon
Given when there are low blood sugar levels (made naturally by the alpha cells of the pancreas), it stimulates the conversion of stored glycogen in the liver to glucose when then can be released into the bloodstream
- stimulates glycogenolysis
Lipolysis
- triglycerides broken down into fatty acids and glycerol
- fatty acids are oxidized into acetyl-coA by beta oxidation
- acetyl-coA then used in Kreb’s cycle
- glycerol directly enters the glycolysis pathway as DHAP
(Because one triglyceride can yield 3 fatty acid molecules with as much as 16 or more carbons in each one, fat molecules yield way more energy than carbohydrates, yield more than twice the amount of energy)
Ketogenesis
- occurs when we lack carbohydrates, begins to use fats as energy source
- oxaloacetate or another intermediate molecule of the kreb’s cycle depletes and therefor acetyl-coA cannot enter the cycle anymore, it begins to build up
- the liver converts acetyl-coA into ketone bodies by ketogenesis
- this leads to ketosis are release of ketone bodies in urine
- most ketone bodies are organic acids —> metabolic acidosis
Examples of ketone bodies
Acetoacetic acid, beta-hydroxybutyric acid and acetone
4 types of tissue
- epithelial
- connective
- muscle
- nervous
Two types of epithelial tissue
covering / lining epithelium - outer layers of the skin, open cavities of the cardiovascular, digestive and respiratory system and encloses ventral body cavity
glandular epithelium - covers the glands (both exocrine an endocrine) of our body
6 main functions of epithelial tissue
protection, secretion, absorption, excretion, filtration, diffusion and sensory reception
Epithelial structure
apical surface and basal surface
Apical surface
upper surface that is exposed to the exterior world or the cavity of an internal organ, may contain microvilli (acts to increase surface area and the efficiency of absorption)
Basal surface
surface for attachment, includes basal lamina and reticular lamina, the bottom edge of the cell or tissue adjacent to the basement membrane
Basal lamina
filters what is allowed to diffuse up from the connective tissue
Basement membrane
A thin, pliable sheet-like type of extracellular matrix that provides the cell and tissue support and acts as a platform for complex signalling, sits between epithelial tissues including the mesothelium, endothelium and underlying connective tissue
Basal and reticular lamina form the basement membrane
Reticular lamina
fibers that reach up from the connective tissue found underneath, this network of collagen fibers “belongs” to the underlying connective tissue providing an anchoring, basal and reticular lamina AKA the basement membrane
Types of epithelia
Simple epithelia or stratified epithelia
- squamous epithelia
- cuboidal
- columnar epithelia
- stratified squamous epithelium
- translational epithelium
simple squamous epithelia
- very thin and permeable
- flat single layer with disc-shaped central
- used to absorption, secretion and filtration
- found in the alveoli of the lungs and in the pericardial, pleural and peritoneal cavities
Two types:
- endothelium - slick and friction reducing lining (capillaries)
- mesothelium - found in serous membranes on the lining of ventral body cavities and covering organs
simple cuboidal epithelium
- single layer of cube like shaped cells
- large spherical central nuclei
- used primarily for secretion and absorption
- found on the surface of the ovaries, lining of nephrons and walls of the renal tubules
simple columnar epithelia
- single layer of tall cells with round to oval shaped nuclei
- might also contain goblet cells
- these epithelia are used for absorption and secretion (some even have cilia on their free surface - cilia moves water relative to the cell in a regular movement of the cilia)
- found in the small intestine where it absorbs nutrients from the lumen of the intestine and found in the stomach
2 modifications of simple columnar epithelia
- dense microvilli on the apical surface of absorptive cells
- tubular glands made of cells that secrete mucous containing intestinal juice
Pseudostratified columnar epithelium
- single layer of cells that have different heights (therefore some do not reach the surface)
- nuclei can be seen at many different levels
- might have mucous-secreting cells
- found along the respiratory airways (ciliated type), non-ciliated found in male sperm carrying ducts of reproduction and in large glands
- mainly involved in absorption and secretion of mucous, use of ciliary action to move mucous, so in the respiratory track it can secret a layer of mucous to trap dust and then the cilia move this sheet of dust trapping mucous up and away from the lungs
Stratified squamous epithelium
- the apical surface are made up of squamous and the deep layers are made from cuboidal or columnar
- provides protection against mechanical stress, chemical abrasions and even radiation
- found in the esophagus, mouth and vagina
- found in areas of wear and tear - external part of the skin and extends a short distance into every body opening that is directly continuous with the skin
Epithelial properties
- polarity - composed of layers
- supported by connective tissues - sits on connective tissue layer collagen protein fibers reach up and the basement membrane / basil layer helps resist stretching and tearing
- avascular but innervated - supplied by capillaries of connective tissue, no blood vessels - nourishment comes from substances that diffuse from blood vessels in underlying connective tissue (innervated by nerve fibers)
- high regenerative capacity - when apical basal polarity are destroyed, epithelial cells begin to reproduce rapidly by cell division, this requires adequate nutrition
simple epithelia
made up of a single cell layer, this type of epithelia is often used where we need to absorb something, for secretion or to filter something, so the thin epithelial barrier is very desirable
stratified epithelia
this is epithelia that is made up of two or more layers of cells which are stacked on top of each other, found in areas that are more likely to be damaged like high abrasion areas such as the lining of the mouth, as this provides more protectiong
translational epithelium
- allows for organs to stretch as they kill - think the urinary organs
- made of stratified layers translational epithelium cells
- it is made up of both stratified squamous and stratified cuboidal
- apical layer depends based on the amount of stretch can be squamous like or dome shaped
- basal layer made of columnar of cuboidal epithelium
- found in renal system - mainly the uterus, bladder and part of the urethra
- lines a space / cavity or inside an organ and can undergo a change in their shape or structure
Glandular epithelial
- glands are classified by 2 sets of traits - where they release their product (endocrine meaning internally secreting or exocrine meaning externally secreting) and the relative cell number - unicellular or multicellular
- made of stratified layers transitional epithelium cells
- a glad is cells that release a product known as a secretion
- endocrine or exocrine
Endocrine glands
- ductless
- secret by exocytosis directly into extracellular space
- hormone produces
Exocrine glands
- secrets products onto the bodies surface or into body cavities
- ducted (multicellular) or ductless (exocytosis done by unicellular glands)
- produce things like mucous, sweat, oil, saliva, bile and digestive enzymes to name a few
Unicellular exocrine glands
- the important unicellular exocrine glands are mucous cells and goblet cells
- found within the epithelial lining of the respiratory and intestinal tracts
- all types of glands produce mucin (which once it becomes dissolved in water forms mucous - a slimy coating, used to protect and lubricate surfaces
- mucous cells - aid in stress / stretch or acidic environments
- goblet cells - aid in immunity
Multicellular exocrine glands
- made up fo two basic parts - epithelium derived duct and secretory unit made up of secretory cells
- the secretory unit is surrounded by connective tissue which supplies it with blood vessels and nerve fibres, this forms a fibrous capsule which enters the gland and divides it into lobes
Multicellular exocrine glands - classified by …
Structure - simple or compounds glands
- simple glands have an unbranched duct
- compound glands have a branched duct
Compound glands - further categorized by their secretory units
- tubular - secretory cells from tubes
- alveolar - secretory cells from small sacs
- tubuloalveolar - if they have both tubular and alveolar units
Multicellular exocrine glands
Secretion:
- merocrine glands - secret their products via exocytosis as it is produced (most common)
- holocrine glands - accumulate their products inside of them until they rupture
- apocrine glands - debated if they are in humans or not, they work like holocrine glands, but the apex of the cell pinches off to releasing secretory granules and a little bit of cytoplasm, unlike holocrine the cell does not die but repairs this damage and continues the cycle
Connective tissue
- most abundant tissue in the body
- made up of 4 different classifications - connective tissue proper, cartilage, bone and blood
- arise from embryonic origin - mesenchyme
- varying degrees of vascularity - cartilage is avascular, dense connective tissue is poorly vascularized and other types are rich in blood supply
- composed of an extracellular matrix mainly non-living, this give it its strength and resilience to trauma
2 main elements of connective tissue …
1 - ground substance
2 - fibres
Connective tissue - ground substance
- fills the space between cells and contains fibres allowing it to be flexible
- ground substance is filled with interstitial fluid and other proteins
- as the ground substance contains a large amount of fluid, it acts like a medium for nutrients and other dissolved substances to disuse through between the cell and the blood capillaries
Connective tissue - fibres types
Collagen - tough and provide tensile strength (these are the strongest and most common), made primarily of collagen in a cross lined fibrils which are bundled together into collagen fibres
Elastic - contains elastin that allows them to stretch and recoil, mainly in skin, lungs and blood vessel walls
Reticular - surround small blood vessels and support soft tissue of organs to allow more “give”, it is made up of a net or network of short fine collagenous fibre (differing slightly in chemical and structural form)
Connective tissue cells
- each major class has its own cell type (primarily blast cells)
- fibroblasts = connective tissue proper
- chondroblasts = cartilage
- osteoblasts = bone
- hematopoietic stem cells = blood
- also contains fat cells, immune cells like macrophages, lymphocytes, mast cells and blood vessels, nerves
Connective tissue - fibroblasts
Fibroblasts can often be seen adhering to newly formed fibres
Connective tissue- macrophages or histiocytes
Play a role in phagocytosis and thereafter enter the lymphatic system to aid in activation of immune responses
Connective tissue - leukocytes
These blood borne defensive cells leave the vascular system during inflammatory events to patrol adjoining tissue spaces
Connective tissue - plasma cells
Highly efficient producers of antibodies
Connective tissue - mast cells
This is the key cell involved in inflammation, mast cells release histamine and heparin, these chemical agents induce the vascular response that cause inflammation
Connective tissue - adipocytes
Are the cells involved in the metabolism and storage of fats or triglycerides
Connective tissue - mesenchymal cells
These are the embryonic stem cells that divide to form new cells of all connective tissue types
“Blast” suffix
Means to be forming and they are the cells that make the ground substance and fibres
“Cyte” suffix
Once the blasts mature, the become less active forms with the suffix “cyte” which help to maintain the health of the matrix
- cytes can revise back to blasts to help with repairs, etc..
Connective tissue proper - loose connective tissue types
Areolar connective tissue
Adipose connective tissue
Reticular connective tissue
Areolar connective tissue
- this is the support network connective tissue that binds to other tissue (provides support for blood vessels and nerves)
- functions - stores nutrient in fat, provides a defence against infection, holds fluid as seen with edema)
- also forms much of the mesentery supporting organs within the abdominal cavity
- as a supportive material for blood vessels and nerves, areolar connective tissue is found in the nooks and crannies of most tissues where blood vessels and nerves penetrate
Edema causes
Due to the areolar tissue becoming inflamed, acting as a sponge and soaking up excess fluids
Adipose connective tissue
- large amount of capillary beds
- much higher nutrient storing capacity vs areolar tissue - this is due to the fact that adipocytes (fat cells) make up about 90% of its mass)
- when we look at adipose tissue under a microscope, we can see the large fat droplet (almost pure triglyceride) taking up almost the whole cell pushing the nucleus off to one side
- can be found in subcutaneous space
- main functions include insulation, nutrient storage and shock absorber
Reticular connective tissue
- form of connective tissue that is used to provide a matrix like soft internal skeleton known as stroma which is used to support free blood cells in lymph nodes, bone marrow and the spleen
- like areolar but has lots of reticular fibres - these form a delicate network in which reticular cells are found
Connective tissue proper - dense connective tissue types
Dense regular connective tissue, dense irregular connective tissue and elastic connective tissue
Dense regular connective tissue
- closely packed bundles of collagen fibres running on the same direction and parallel to direction of pull
- great for use in areas where you need good resistance to tension in one direction
- the slightly wavy appearance of the fibres allow for a little bit of stretch in the tissue but one these fibres are pulled straight there is no more stretch
- it is very poorly vascularized and has very few other cells then its fibroblasts (which are between the collagen fibres and continuously produce the fibres)
- forms tendons, fascia around muscles and blood vessels
Dense irregular connective tissue
- same structural element as regular, but fibres run in more than one plane (irregularly) and the collagen fibres are much thicker
- forms the dermis, joint capsules coverings around some organs
- areas where tension is applied from more than one direction
Elastic connective tissue
Dense regular connective tissue with high proportion of elastic fibres
- allows recoil of tissues following stretch
- found in walls of arteries, bronchial tubes, vertebral ligaments
Cartilage
- flexible connective tissue that keeps joint motion fluid by coating the surfaces of the bones in our joints and by cushioning bones against impact
- good at withstanding tension and compression
- avascular - it gets nutrients from blood vessels found in the connective tissue membranes surrounding it via diffusion
- no nerve fibres
Types of cartilage found in the body
Hyaline, elastic and fibrocartilage
Cartilaginous tissue
- embedded within the cartilage matrix are chondrocytes, or cartilage cells, and the space they occupy are called lacunae (singular = lacuna)
- cartilaginous tissue is avascular, meaning that all nutrients need to diffuse through the matrix to reach the chondrocytes
- this is a factor contributing to the very slow healing of cartilaginous tissues
Hyaline cartilage
- the most common cartilage in our body
- provides a pliable but firm support and covers (articular cartilage) long bone ends, nose, ribs, respiratory passages and epiphyseal plates
- has smooth surface
- makes up a template of the embryonic skeleton before bone formation
- strong and flexible, it is found in the rib cage and nose and covers bones where they meet to form moveable joints
Epiphyseal plates
A plate of hyaline cartilage at the ends of bone allows continued growth until adulthood
Fibrocartilage
- it is “in between” of hyaline cartilage and dense regular connective tissue
- tough because it has thick bundles of collagen fibres dispersed through its matrix
- the knee, jaw joints and intervertebral discs are examples of fibrocartilage
- compression and resists tension
- supports heavy pressure
Elastic cartilage
- nearly identical to hyaline but more elastic fibres
- this tissue gives rigid support as well as elasticity
- will go back to its original shape
- example - ear, epiglottis
Bones
- hardest connective tissue
- formed by a rigid extracellular matrix of collagen fibres that have a mineralized substance with a type of calcium phosphate
What would happen to bone without collagen?
Without collagen, bones would be brittle and shatter easily
What would happen to bone without mineral crystals
Bones would flex and provide little support
Blood - connective tissue
- type of atypical connective tissue which has no fibres but is a fluid tissue
- erythrocytes (aka red blood cells) - transports
- leukocytes (aka white blood cells) - immune system defence cells protect against micro-organisms or molecules
- some leukocytes are able to move across the endothelial layer of the blood vessels to enter other tissue
- platelets involved in clotting
- soluble protein molecules that form the “fibres” during clot formation
- rest is a mix of nutrients, salt, waste all dissolved in liquid matrix
Classifications of muscle
Skeletal, cardiac and smooth muscle
Characterizations used for muscle
Characterized by properties that allow movement
- excitable and respond to stimulus
- contractile - can shorten and generate a pulling force
- voluntary - under conscious control
- involuntary - are not under conscious control
Skeletal muscle
- voluntary control
- muscles are made up of skeletal muscle cells pack together with connective tissue
- skeletal muscles generate heat as a by-product of their contraction and thus participate in thermal homeostasis - shivering is an involuntary contraction of skeletal muscles in response to perceived lower than normal body temperature
Skeletal muscles under the microscope
Long and cylindrical
Multi-nuclei
Striated because of myofilaments
Cardiac muscle
- found only in the walls of the heart
- involuntary control - ability to contract with their own intrinsic rhythms (no need for any stimulus)
- cardiomyoctes attach to each other using special cell junctions called intercalated discs
- long branching fibres allow for electrochemical and mechanical sync so the cells can synchronize their actions
Cardiac muscle cells under the microscope
- striated with generally one nucleus
- intercalated discs - anchoring sites (fascia adherens and desmosomes) and gap junctions - gap junctions allow action potentials to travel between cells by allowing ions to move between cells
Smooth muscle
- found in walls of hollow organs other than the heart
- used to squeeze substances through these organs (intestines - peristalsis)
- under involuntary control
Smooth muscle under the microscope
- no visible striations - known as smooth
- spindle shaped with one central nucleus
- together they form a sheet
Nervous tissue
- main components of the nervous system - brain, spinal cord, nerves
- neutrons are branching cells that are made of cell body, axon and dendrite
- respond to stimuli and transmit electrical impulses
Two main types of cells that make up of nervous tissue
1 - neurons - send information via electrochemical impulses called action potentials
2 - supporting cells (such as neuroglia or glial cells) - essential to supporting neurons and modulating propagation
Neuroglia
Play as essential role in supporting neurons and modulating their information propagation
Glia
Also called glial cells or neuroglia, they are non-neuronal cells in the CNS and the PNS, they maintain homeostasis, produce myelin and provide support and protection
Regeneration - tissue repair step 2
3 steps to tissue repair - inflammation, organization and regeneration
Organization - begins during inflammatory phase, about 3-4 days after injury, granulation tissue replaced blood clot, capillaries are contained in the granulation tissue, fibroblasts in granulation tissue product collagen fibres that bridge the gap of the wound, surface epithelial begin to multiply and migrate over granulation tissue
Regeneration - tissue repair phase 1
Inflammatory phase - begins at the time of the injury and lasts up to 4 days, includes clotting of platelets to stop blood loss, mast cells are released, release of vasodilator histamines to increase blood flow to the area
Regeneration - tissue repair stage 3
Regeneration phase - epithelial surface regenerates under scab, thickens, this phase can continue for 6 months to one year after injury, collagen continues to increase and the tissue begins to contract with the help of fibroblasts, both of which add strength to the new tissue, excessive collagen can cause soar tissue formation
Four signs of inflammation
Redness, swelling, pain and local heat
Debris is removed slowly during tissue repair by …
The lymphatic system
Tissue regeneration capacity
Extremely well - epithelial, bone, areolar connective tissue, dense irregular connective tissue, blood forming tissue
Moderate capacity - smooth muscle, dense regular connective tissue
Weak capacity - skeletal muscle, cartilage
No capacity - cardiac muscle, nervous tissue in the brain (replaced by scar tissue which lacks flexibility and is more compact)
Three layers of the integumentary system
1 - epidermis
2 - dermis
3 - hypodermis
Epidermis
- the most superficial layer of your skin
- made of epithelial cells
- has no vascularization
Dermis
- mostly fibrous connective tissue
- has vascularization within this layer
Hypodermis
- technically not part of the skin
- deep to the dermis (holds subcutaneous tissue)
- this layer shares the skins protective functions however, it is functionally not part of the skin
- hypodermis also known as the superficial fascia - made up of mostly adipose tissue and stores fat and is an anchor for the skin to the underlying structures
Keratinocytes
- main job is to produce keratin - a fibrous protein that helps give the epidermis protective properties
- comes from the stratum basale - undergoing mitosis and are pushed up
- the layer of keratinocytes are held together tightly by desmosomes
- as they move up by new cell production under them they product keratin
- at the surface of the skin they are dead, keratin filled plasma membranes
Melanocytes
- synthesizes pigment melanin
- melanin accumulates in membrane bound granules known as melanosomes
- the granules of melanin accumulate on the superficial side of the keratinocyte nucleus to make a pigment shield to protect from UV
- melanosomes are then moved to keratinocytes
Dendritic cells
- ingest foreign substances
- key activator of our immune system
Tactile (markel) cells
- found at the epidermal-dermal junction and are associated with disc-like sensory nerve endings
- tactile cells with the sensory nerve ends function as sensory receptors for touch
The epidermis layers
Stratum basale, stratum spinosum, stratum granulosum, stratum lucidum and stratum corneum
Epidermis - stratum basale
- deepest layer, attaching to the dermis
- made up of the youngest of the keratinocytes
- basal cell divide here (stratum germinativum) - when the basal cell divides in the stratum basale one cell will go up to become the mature keratinocyte and the other will remain to produce more keratinocytes
- melanocytes (reach into more stratum spinosum and occasionally tactile cells are found here)
Epidermis - stratus spinosum
- contains a weblike system of bundles of pre-keratin intermediate filaments to resist tension
- these filaments attach to desmosomes and look like spiked balls
- melanin granules and dendritic cells are most abundant in this layer
Epidermis - stratum granulosum
- keratinization occurs at this layer - process in which the cytoplasm of the epidermis is replaced by keratin
- cells flatten and nuclei and organelles begin to disappear and disintegrate
- accumulate 2 granules (keratohyaline grandules - which helps to form keratin in the upper layer and lamellar granules - helps to slow water loss in the epidermis as it contains water resistant glycolipid)
- the cell’s plasma membranes also thicken due to proteins binding inside layer of their membrane and the lipids that were released by the lamellar granules coat the outside surface - this leads to waterproofing and more physical toughness)
- layer of death
Epidermis - stratum lucidum
- visible only in thick skin
- made up of 2-3 rows of clear, flat, dead keratinocytes
- found here or in the Stratum Corneum the sticky substance of the Keratohyaline granules clings to the keratin filaments in the cells, this causes them to form large cable like parallel arrays of intermediate filaments (tonofilaments)
Epidermis - stratum corneum
- makes up the majority of the epidermal thickness
- this layer protects against abrasions and damage to the skin (via keratin and thickened plasma membranes)
- the glycolipids between cells waterproofs this layer
- cells at this layer are dead
- made of flattened anucleated (no nucleus) cells
- during a specialized form of apoptosis, the nucleus and other organelles break down, but the plasma membrane thickens
- made up of a protective coat of keratin and the thick plasma membranes of the cells
Thick epidermis
- used in areas that are likely to experience abrasion (palms, fingertips and soles of the feet)
- made of 5 layers of strata - stratum: basale, spinosum, granulosum, lucidum, corneum
- stratum corneum particularly dense in these locations
Thin epidermis
- found most everywhere else on the body
- all layers are thinner than thick skin
- missing the stratum lucidum
The dermis contains
- two layers - papillary and reticular layers
- contain fibroblasts, macrophages, mast cells, white blood cells and lots of vascular / lymphatic and nerve supplies
- made from strong and flexible connective tissue
- hair follicles, oil and sweat glands come from this layer (pushing up and through the epidermis)
The papillary layer
- superficial to the reticular layer
- made of loose areolar connective tissue - collagen and elastic fibres forming a loose mesh, woven with many fine blood vessels, its looseness allows phagocytes and other defensive cells to move freely on “patrol”
- has projections into the stratum basale of the epidermis known as dermal papillae
- in thick skin - dermal papillae are on top of dermal ridges, which collectively form friction ridges (finger prints)
- some have capillary loops, others have free nerve endings (for pain) and touch receptors
The reticular layer
- deep to the papillary layer
- thick vs the thin papillary layer
- made of dense irregular fibrous connective tissue, collagen and elastin fibres, which make up a tight mesh work of fibres
- well vascularized with sensory and sympathetic nerve supply
- this layer makes up about 80% of the thickness of the dermis
What determines the pigmentation of the skin?
Melanin (made in your skin), carotene and hemoglobin
What gives us a suntan?
Melanin, prolonged sun exposure causes melanin buildup which helps protect DNA of skin cells from UV radiation
Where does fair skin’s pinkish hue come from?
Oxygenated pigment
Why does it take time for a tan to appear from sun exposure?
Take 10 days after initial sun exposure for melanin production to peak
Melanin in light coloured skin…
Small amounts of melanin in light coloured skin, so epidermis is nearly transparent and allows hemoglobin’s colour to show through
Why do sun tans fade after time?
- melanosomes are temporary structures - which are eventually destroyed by fusion with lysosomes
- the melanin filled keratinocytes (found in the stratum corneum) slough off over time)
What makes different skin tones if we have the same number of melanocytes (cells)?
It’s the kind of melanin made and the amount of melanin made / retained
Melanin
- made up of amino acids
- ranges in colour from reddish yellow to brownish black
- melanin pigment is int he deeper layer of the epidermis
- the melanosomes (that hold the pigment) are broken down by lysosomes higher up so that why’s the pigment is found in the deeper layers
- the darker the skin the darker the colour and more melanosomes you have vs fair skinned individuals - keratinocytes are retained longer with darker skin
Skin appendages
Nails, hair, sebaceous gland, sweat glands
What are nails made from?
Made out of hard keratin vs the soft keratin of the epidermis
Each nail has ..
- a free edge
- an nail palate / body
- proximal root
Nails
- the nail bed is made of the deeper layers of the epidermis and the actual nail is the superficial keratinized layers
- nail growth occurs at the nail matrix, the thick proximal portion of the nail bed
- the hyponychium (informally known as the quick) found at the distal free edge secures the nail’s free edge to the fingers
What can the nail tell us?
Concave nail - iron deficiency
Horizontal lines - malnutrition
Clubbing of the nail - lung cancer, COPD, interstitial lung disease, GI disorders, some autoimmune disease
Yellow colour to the nail - respiratory or thyroid disorder
White / yellow thick nails - fungal infection
Hair
- made by the hair follicles out of mostly dead keratinized cells
- hair’s main function is - sense insect, etc.. on the skin, on the scalp - guards head from trauma, heat loss and sunlight, eyelashes shield the eyes, nose hairs filter large particles
Hair structured elements
Shaft - projects from the skin, this is the part where keratinization has already completed
Root - remained deep in follicle and the location where keratinization is still occurring
Vascular supply
Sebaceous gland - lubricates and keeps hair from dying
Arrest or pili muscle - causes the hair to stand erect
Sebaceous gland
- branched alveolar glands
- function is to secrete sebum (oily substance)
- most are found as outgrowths around hair follicles, found everyone on the body except thick skin on the soles of the feet and the palms of the hands
- larger on the face, neck and upper chest
- purpose is to serve as lubrication for hair and skin so it does not become brittle and slows water loss from skin when air humidity is low, sebum also kills bacteria
Sweat (sudoriferous) glands
- up to 3 million per person
- found everyone on the body except the nipples and parts of the external genitalia
- function is to control body temperature
- sweat is a hypotonic filtrate of the blood made of 99% water and some salts as well as antibodies, dermicidin and vitamin C and some traces of metabolic waste
Sweat and drugs
Some drugs that are taken can be found in small amounts within the sweat because of this, therefore, when a person is suspected of being a mule for cocaine officers will often swab the inside of their shoes and test that for traces of cocaine with could have leached out of the balloons they have swallowed
Sweat pH
Normally acidic with a pH of 4-6
Two types of sudoriferous glands
Eccrine (also known as mesocrine sweat glands)
- simple coiled tubular gland
- produces sweat - expels from a funnel-shaped pore
- found most everywhere on the body
Apocrine
- found in the auxiliary and genital regions
- produces the same components that make up sweat as well as fatty substances and proteins
- ducts empty into hair follicles
- the viscous milky substances (made up of fats and proteins) does not smell until bacteria found on the skin gain access to it, they do not begin to function until around the time of puberty
- activated by the SNS, function is still not exactly known, there is a theory they might be the human equivalent of sexual scent glands due to the fact the SNS activates them and they enlarge and shrink during different different phases of the female menstrual cycle
What are the skin’s main functions?
- cutaneous sensation (tactile and pain receptors)
- metabolic functions (such as when the sun hits the skin and converts modified cholesterol into a vitamin D precursor)
- blood reservoir (can hold about 5% of the bodies blood volume)
- excretion (sweat contains a lot of nitrogen waste, water and sodium chloride)
- protection
- temperature regulation
Skin - protection functions
The skin protects as a barrier from the outside world …
Chemicals - using skin secretions (the acid mantle which maintains a low pH), defensins (antibiotic) and melanin
Physical - a physical barrier to stop things from getting into our body however some substances can penetrate the skin
- lipid soluble substances (oxygen, CO2, vitamins A, D, E, K and steroids)
- oleoresins - plant poisons
- organic solvents - acetone, paint thinners, dry cleaning chemicals
- salts of heavy metals (such as lead and mercury)
- select drugs
Biological - has an immune system function to protect us from foreign bodies (dendritic cells trigger parts of the immune system response, dermal macrophages “antigen presenters”)
Skin - temperature regulation
- average amount of sweat loss = 500 mL
- when external environment is cool, blood vessels in skin constrict which causes warm blood to bypass skin and skin temperature drops to external environment)
- this allows passive heat loss to slow and conserve
- hair stands up to keep heat trapped into skin when cool
Aging skin
- rate of epidermal cell regeneration / replacement slows, and the skin begins to thin
- lubricating substances begin to become deficient thus the skin becomes dry and itchy
- less collagen fibres are found in the skin and those that are in the skin become stiffer
- melanocytes reduce in number
Aging skin and UV rays
- increased risk of cancer
- by avoiding UVA (aging rays) - activates an enzyme matrix metalloproteinases which degrades collagen and other dermal components) and UVB (burning rays) helps reduce wrinkles
- the UV rays that we like to call a tan also cause sagging blotchy wrinkled skin with liver spots due to UVA activating that enzyme matrix metalloproteinases which degrades collagen and other dermal components
What are some things we might see when the skin is trying to tell us something?
- cyanosis
- redness, flushing, erythema
- pallow
- jaundice
Hypoxia indicated by the skin
- bluish colouring of the skin that indicates hypoxemia
- unoxygenated hemoglobin in the capillaries generates the dark blue colour appreciated clinically as cyanosis
- with darker skin colours, the melanin masks the changes in skin colour, but cyanosis will still appear in mucous membranes or nail beds
Hypoxia vs hypoxemia
Hypoxia is to low of O2 to sustain normal life functions
Hypoxemia is low O2 in arterial blood
- these are often used interchangeably
Erythema
- redness or flushing of the skin or mucous membranes due to hyperaemia (increased blood flow with dilated capillaries)
- early signs of alcohol abuse is a persistently red face due to enlarged blood vessels (regulation of vascular control in the brain fails with sustained alcohol intake) - referred to as telangiectasia
- can be due to embarrassment, fever, hypertension (the condition itself or side effect of medication), inflammation, allergy
Pallor of the skin
- paleness of blanching of the skin
- caused by - poor perfusion, hypovolemia, anemia, hypoglycaemia, frost bite), not related to melanin but blood flow
- may be hard to see in people with darker skin - have to look at mucous membranes (eyelids and lips)
- hypoglycaemia- andrengeric cutaneous vasoconstriction
Jaundice
- result of bilirubin build up in the blood and tissue - this is a waste produce created when red blood cells break down, builds up particularly in connective tissues and elastin
- this buildup leads to the appearance of jaundice and is caused by any condition that disrupts the flow of bilirubin from the blood to the liver and than out of the body
- damage to the liver - hepatitis, alcoholism and cancer
- interference with the flow of bile - cancer, gallstones, blocking bile duct
- destruction of red blood cells (hemolysis) - toxins
Burns
- burns are tissue damage that results from heat, overexposure to the sun or other radiation or chemical or electrical contact
- burns can be minor medical problems or life-threatening emergencies
- treatment of burns depends on the location and severity of the damage
Burn depth
- traditional classification of burns is first, second, third or fourth degree
- current designations of burn depth are superficial, superficial partial thickness, deep partial thickness and full thickness
- fourth degree is still used to describe the most severe burns, burns that extend into the muscle, bone and / or joints
First degree / superficial burn
- involves only the outer layer of the skin, the epidermis
- the burn site is red, painful, dry but has no blisters (ex. Mild sunburn, long term tissue damage is rare)
- heals in about six days without scarring
Process of first degree / superficial sunburn healing..
Day 1 - redness, hot to touch and painful
Day 2-3 - the pain and erythema subsides
Day 4-6 - the injured epithelium peels away from the newly healed epidermis
Second degree / superficial partial thickness burns
- involves the epidermis and part of the lower layer of the skin, the dermis
- the burn sites looks red, blistered, and may be swollen and painful (forms blisters within 24 hours between the epidermis and the dermis)
- initially appears to be only epidermal may be determined to be partial thickness 12-24 hours later
- heals in 7-21 days, scarring is unusual, pigment changes may occur
- a layer of fibrinous exudates and necrotic debris may accumulate on the surface, which may predispose the burn wound to heavy bacterial colonization and delayed healing
- these burns typically heal without functional impairment or hypertrophic scarring
Second degree / deep partial thickness burns
- extends into the deeper dermis and are characteristically different from superficial partial thickness burns
- deep burns damage hair follicles and glandular tissue
- painful to pressure only, almost always blister (easily unroofed), are wet or waxy dry and have variable mottled colourization from patchy cheese white to red
- they do not blanch with pressure
- if infection is prevented and wounds are allowed to heal spontaneously without grafting, they will heal in 3-9 weeks
- these burns invariable cause hypertrophic scarring
Third degree / full thickness burn
- extends through and destroys all layers of the dermis and often injure the underlying subcutaneous tissue
- burn eschar, the dead and denatured dermis, is usually intact, es-CAR is dead tissue that sheds or falls from the skin
- the eschar can compromise the variability of a limb or torso if circumferential
- skin appearance can vary from waxy white to leathery gray to charred and black
- the skin is dry and inelastic and does not blanch with pressure
- hairs can easily be pulled from hair follicles, vesicles and blisters do not develop
- the eschar eventually separates from the underlying tissue and reveals an unheralded bed of granulation tissue
Fourth degree burn
- deep and potentially life threading injuries that extend through the skin into the underlying tissues such as fascia, muscle and / or bone
- there is no feeling in the area since the nerve endings are destroyed
Cellulitis
- a common, potentially serious bacterial skin infection
- the affected skin appears swollen and red and is typically painful and warm to the touch
- cellulitis usually affects the skin on the lower legs, but it can occur in the face, arms and other areas, it occurs when a crack or break in your skin allows bacteria to enter
- left untreated, the infection can spread to your lymph nodes and bloodstream and rapidly become life threatening, it’s usually spread from person to person
Necrotizing fasciitis
Flesh-eating bacteria is a rare infection of the skin and tissues below it, it can be deadly if not treated quickly
- necrotizing fasciitis spreads quickly and aggressively in an infected person, it causes tissue death at the infection site and beyond
Decubitus ulcers
- bedsores - also called pressure ulcers - are injuries to the skin and underlying tissue resulting from prolonged pressure on the skin
- bedsores most often develop on skin that covers bony areas of the body, such as the heels, ankles, hips and tailbone
Abscess
A tender mass generally surrounded by a coloured area from pink to deep red, abscesses are often easy to feel by touching, the vast majority of them are caused by infections, inside, they are full of puss, bacteria and debris. They are painful and warm to touch, abscesses can show up any place on your body
Urticaria (hives)
Reddened, itchy welts that may be triggered by exposure to certain foods, medications or other substances
Hematoma
Collection of blood outside of a blood vessel, it occurs because the wall of a blood vessel wall, artery, vein or capillary has been damaged and blood has leaked into tissues where it does not belong
The nervous system has 3 main overlapping functions …
1 - sensory inputs - with the use of millions of sensory receptors out body monitors for changes both inside and outside of our body (sensory inputs)
2 - integration - we then process and interpret these sensory inputs and made a decision as to what should be done (called integration)
3 - motor output - we can affective effector organs (muscles and glands) in order to perform a response (known as motor output)
Divisions of the nervous system…
CNS and PNS
CNS —> brain and spinal cord
PNS —> motor and sensory neurons
Motor neurons —> somatic nervous system and autonomic nervous system
Autonomic nervous system —> sympathetic division and parasympathetic division
PNS
- everything outside of the CNS, nerves that run from the brain and spinal cord
- the PNS is divided into two divisions - sensory division (afferent) and motor division (efferent)
Sensory division of PNS
Afferent
Carries messages (impulses) towards the CNS from receptors all over your body
Made up of somatic sensory fibres and visceral sensory fibres
Motor division of PNS
- efferent
- carries messages (impulses) from the CNS to effector organs (muscles and glands)
- made of the somatic nervous system (voluntary) and the autonomic nervous system (involuntary)
Somatic nervous system of motor division of PNS
- somatic motor nerve fibres carry messages from the CNS to skeletal muscles to allow conscious control of movements
Autonomic nervous system of the motor division of PNS
Visceral sensory impulses from the visceral organs (organs within the ventral body cavity) and glands
- involuntary control
- has two divisions —> sympathetic and parasympathetic
Parasympathetic control —> rest and digest
- constricts pupils
- stimulates salivation
- inhibits heart
- constricts bronchi
- stimulates digestive activity
- stimulates gall bladder
- constricts bladder
- relaxes rectum
Sympathetic system —> fight or flight
- dilates pupils
- inhibits salivation
- relaxes bronchi
- accelerates heart
- inhibits digestive activity, stimulates glucose release by liver
- secretion of epinephrine and norepinephrine from kidney
- relaxes bladder
- contracts rectum
Neurons
- a specialized cell that is used to conduct electrical impulses (messages) around the body
- our nervous system is made up of 2 principal types of cells the neurons and neuroglia
3 special characteristics (besides conducting messages) or neurons …
- amitotic - they are unable to divide
- have a very high metabolic rate requiring a large amount of oxygen and glucose (they can not survive more than a few minutes without oxygen)
- extreme longevity - can function optimally for your whole lifetime
Why do neurons not have centrioles?
Neurons cannot divide because they lack centrioles, because centrioles function in cell division, the fact that neurons lack these organelles is consistent with the amniotic nature of the cell
- some cells in the human body never divide and one such cell is the neuron
- these are times / locations when we can develop new neutrons in adulthood, this originate as stem cells
Cell body of the neuron
- the cell body is the main centre of the neuron cell which has the normal organelles that are needed to synthesize proteins and other chemicals
- is it also known as the soma
- a cluster of cell bodies in the CNS is known as nuclei (this is where most neutron cell bodies are located)
- cell bodies that lie along nerves in the PNS are called ganglia
- extending from cell bodies are arm like processes - dendrites and axons
Dendrites
The main receptive region of the neuron and transmit the message toward the cell body (graded potentials not action potentials), they provide a large surface area for receiving signals
- are always non-myelinated
Axon
- single part of the cell that conducts messages away from the cell body and towards the axon terminals
- a neuron only has one axon by they might branch along their length (axon collaterals)
- comes from the axon hillock on the cell body - the trigger zone
- can be long accounting for almost the entire length of the neuron, short or absent (long axons are called nerve fibres)
- the distal end of the axon is the axon terminal or axon boutons
- the axon is the site of nerve impulse generation and transmission
- may of may not have myelin sheath - white fatty covering that protects and insulates the axons, creating nodes of ranvier which increases conduction velocity of the axon
Neuroglia (glial cells)
- there are 6 types of neuroglia (4 in CNS and 2 in PNS)
- do not produce electrical impulses, they maintain homeostasis, form myelin in the peripheral nervous system and provide support and protection for neurons
Astrocytes
- the most abundant and versatile glial cell
- found in the CNS, the facilitate the exchange between the neuron and the capillaries
- they maintain the chemical environment around the neurons and anchor / facilitate the exchange between neurons and capillaries, their role as exchange facilitators helps to determine the capillary permeability for neurons
- helps to clean up leaking K ions and recycle transmitters, this ensures the outside environment of the neuron is kept in a functional balance
Microglia
- found in the CNS, they maintain the health and defence of the neurons
- when they detect a foreign micro-organism or dead neurons they turn into a special macrophage in order to phagocytize it, which is critical as our immune cells have limited access to the CNS
- they are like the guards or security
What are the four glial cells of the CNS?
Astorcytes, microglia, ependymal cells and oligodendrocytes
What are the glial cells of the PNS?
Satellite cells and Schwann cells
Ependymal cells
- found in the CNS, these cells line the central cavities of the CNS to help with the movement of cerebrospinal fluid (CSF)
- they are ciliated and use the beating of their cilia to circulate the CSF
Oligodendrocytes
- found in the CNS
- form the myelin sheaths of the CNS
Satellite cells
- found in the PNS
- surround the neuron cell bodies and are thought to have similar functions to the astrocytes in the CNS
Schwann cells
- found in the PNS
- form the myelin sheath of the PNS
- play a vital role in regeneration of damaged peripheral nerve fibres
3 structural class of neurons
Unipolar (pseudo) neurons, bipolar neurons, and multipolar neurons
Pseudo, unipolar neurons
- found in the ganglia in the PNS function as sensory neurons
- a single process extending from the cell body and divide into 2 branches that is associated with a receptor at the distal end, known as the peripheral process and a central process that goes into the CNS
Bipolar neurons
- they are pretty rare in the body but are found in special sense organs such as neurons in the retina of the eye or the olfactory mucosa
- has 2 processes, one from single axon and one from dendrite
Multipolar neurons
- most common neuron type in humans, more than 99% of neurons are multipolar and it is the major neuron of the CNS
- they have 3 or more processes, one axon and multiple dendrites
- many processes extend from the cell body, all are dendrities except for a single axon
3 functional classes of neurons
- sensory (afferent) neurons - conduct impulses towards the CNS from receptors, almost all unipolar with cell bodies in the sensory ganglia outside of the CNS, the receptor end of some sensory neurons have terminals that function as the actual sensory receptors but most sensory neuron endings have receptors to provide them with information
- motor (efferent) neurons - conduct impulses from the CNS to effectors (muscles and glands), these are multipolar and except for some neurons in the ANS they have their cell bodies found in the CNS
- inter neurons - associated neurons, conduct impulses between sensory and motor neurons and are the CNS integration pathways, these make up 99% of out neurons and are multipolar, most found within the CNS
Functional class - neuron type according to direction of impulse conduction …
Multipolar neurons - most are inter neurons that conduct impulses within the CNS, integrating sensory input or motor output, may be one of a chain of CNS neurons or a single neuron connecting sensory and motor neurons
- some are motor that conduct impulses along the efferent pathway from the CNS to an effector (muscle / gland)
Bipolar neurons - essentially all are sensory neurons located in some special sense organs (ex. Bipolar cells of the retina)
Unipolar neurons - most are sensory neurons that conduct impulses along afferent pathways to the CNS for interpretation, these sensory neurons are called primary or first order sensory neurons)
Membrane ion channels
- there are lots of different membrane proteins, which acts as ion(s) channels in order to allow ions in and out of the cell, on a selective bases only allows their type of ions to pass
- of these there are many membrane ion channels - non-gated aka leaky (always open) and gated (to be gated means that it has a gate made of protein which will change shape in order to open and close the channel)
- ion channels are used to produce an electrical current by ions diffusing across the membrane with their concentration gradient
There are many different types of gated ion channels within their cell ..
Chemically gated (ligand gated) - open with the appropriate chemical binds, neurontransmitter will bind and it causes the channel to open Voltage gated - channels open in response to a change in membrane potential Mechanically gated - channels open when a membrane receptor is physically deformed, pressure applied causes it to open
The resting membrane potential
- salty banana - there is more sodium on the outside of the cell and more potassium inside of the cell
- polarized membrane have a net positive charge outside and a net negative charge inside therefore a -70 mV across the membrane (this is a negative charge relative to the outside of the cell)
- the potential difference of the resting neuron is known as the resting membrane potential
- more permeability to potassium leaking to the resting potential
- sodium and potassium pump work to maintain polarized state of diffusion gradient
Sodium / potassium pump
Maintains the polarized state by maintaining the diffusion gradient for sodium and potassium, it does this by pumping 3 sodiums from the cell and returning 2 potassium’s back into the cell (for each cycle of the pump, which is always running)
