Human Physiology Flashcards
Alimentary Canal
An alimentary canal is a group of organs through which food actually passes (oesophagus, stomach, small intestine and large intestine)
What is the oesophagus?
- A hollow tube connecting the oral cavity to the stomach
- Epiglottis separates the oesophagus from the trachea
- Food is moved in a bolus via the action of peristalsis
What is the stomach?
- Temporary storage tank where food is mixed by churning and protein digestion begins
- The pH of the gastric juices released by the stomach is around 2
What is the small intestine?
- Long, highly folded tube where usable food substances (nutrients) are absorbed
- Small intestine consists of three sections: the duodenum, jejunum and ileum
What is the large intestine?
- Large intestine is the final section of the alimentary canal, where water and dissolved minerals (i.e. ions) are absorbed.
- sections that make up the large intestine are the ascending / transverse / descending / sigmoidal colon, as well as the rectum
Accessory Organs
Accessory organs aid in digestion but do not actually transfer food
What are the salivary glands?
- release saliva to moisten food and contain enzymes
- three salivary glands are the parotid gland, submandibular gland and sublingual gland
What is the pancreas?
- pancreas produces a broad spectrum of enzymes that are released into the small intestine via the duodenum
- pancreas secretes certain hormones (insulin, glucagon), which regulate blood sugar concentrations
What does the liver do?
- takes the raw materials absorbed by the small intestine and uses them to make key chemicals
- roles of the liver include detoxification, storage, metabolism, bile production and haemoglobin breakdown
Gall Bladder:
- gall bladder stores the bile produced by the liver (bile salts are used to emulsify fats)
- Bile stored in the gall bladder is released into the small intestine via the common bile duct
Chewing (Mouth)
- initially broken down in the mouth by the grinding action of teeth
- tongue pushes the food towards the back of the throat, where it travels down the esophagus as a bolus
- epiglottis prevents the bolus from entering the trachea, while the uvula prevents the bolus from entering the nasal cavity
Churning (Stomach)
- stomach lining contains muscles which physically squeeze and mix the food with strong digestive juices
- Food turns into creamy paste called chyme
- chyme enters the small intestine
Peristalsis
The movement of food through the alimentary canal via contraction and relaxation of longitudinal smooth muscle
Segmentation
The contraction and relaxation of non-adjacent segments of circular smooth muscle in the intestines to mix food with digestive juices
Chemical Digestion
food is broken down by the action of chemical agents.
Stomach Acids
- the acidic environment (pH 2) is to Denature proteins and other macromolecules, aiding in digestion
- the mucous membrane in the stomach epithelium prevent acids from damaging the gastric lining
- Pancreas release alkaline compounds to neutralize the acids in the intestine
Bile
- Fluid produced in the liver stored in the gall bladder
- Bile salts interact with fat globules (lipids) and divide them into smaller droplets (emulsification) to help increases the total surface area available for enzyme activity
Enzymes
Biological catalysts that speed up chemical reactions
Small Intestine
The small intestine absorbs usable food substances
Large Intestine
The large intestine absorbs water and dissolved minerals
Structure of the small intestine
- Serosa – a protective outer covering composed of a layer of cells reinforced by fibrous connective tissue
- Muscle layer – outer layer of longitudinal muscle (peristalsis) and inner layer of circular muscle (segmentation)
- Submucosa – composed of connective tissue separating the muscle layer from the innermost mucosa
- Mucosa – a highly folded inner layer which absorbs material through its surface epithelium from the intestinal lumen
Villi
folded projections of the inner epithelial lining which help to increase surface area for absorption of the digested products.
MR SLIM (features of villi)
- Microvilli – Ruffling of epithelial membrane further increases surface area
- Rich blood supply – Dense capillary network rapidly transports absorbed products
- Single layer epithelium – Minimises diffusion distance between lumen and blood
- Lacteals – Absorbs lipids from the intestine into the lymphatic system
- Intestinal glands – Exocrine pits (crypts of Lieberkuhn) release digestive juices
- Membrane proteins – Facilitates transport of digested materials into epithelial cells
Villus Epithelium
- Tight Junctions - create an impermeable barrier and keep the digestive fluids separated to maintain a concentration gradient
- Microvilli - Increase Surface Area
- Mitochondria - Epithelial cells of intestinal villi will possess large numbers of mitochondria to provide ATP for active transport mechanisms
- Pinocytotic Vesicles - non-specific uptake of fluids and dissolved solutes
Absorption
- Tight junctions between epithelial cells occlude any gaps between cells – all monomers must cross the membrane
- Different monomers undertake different methods for crossing the apical and basolateral membranes
Types of Transport across membrane
- Secondary Active Transport
- Facilitated Diffusion
- Osmosis
- Simple Diffusion
Bulk Transport
Endocytosis is a process that creates internal vesicles containing extracellular material by invaginating the plasma membrane, which is energy-dependent. Pinocytosis in the intestines involves the formation of vesicles around fluid-containing dissolved materials, allowing the ingestion of materials en masse more quickly than via membrane proteins.
Maltose and Dextrin
- Both maltose and dextrin are digested by enzymes (maltase) which are fixed to the epithelial lining of the small intestine
- The hydrolysis of maltose / dextrin results in the formation of glucose monomers
Pancreas Functions in Starch Breakdown
They Produce amylase and hormones through exocrine glands (amylase) and endocrine glands (hormones)
Insulin and Glucagon in Blood Glucose Regulation
They help to regulate glucose concentrations in the bloodstream.
- Insulin is able to do this by increasing glycogen synthesis and storage in the liver and adipose tissues.
- glucagon is able to do this by limiting the synthesis and storage of glycogen by the liver and adipose tissues
Function of atria
Collect blood returning to the heart via veins and pass it on to the ventricles
function of the ventricles
Pump blood out of the heart at high pressure via arteries
What is the function of the left side of the heart?
Pump oxygenated blood around the body (systemic circulation) so it has ticker muscular walls
What is the function of the right side of the heart?
Pump deoxygenated blood to the lungs (pulmonary circulation)
function of arteries
- Convey blood at high pressure from the heart ventricles to the tissues of the body and lungs
- Luman is narrow with thick walls to allow for high-pressure movement without rupturing
- It contains an inner layer of muscle and elastic fibres (collagen) to help maintain pulse flow by contracting and stretching.
How does blood flow through arteries?
In repeated surges called pulses at a high pressure, which is maintained between pumps by muscle and elastic fibres
muscle fibres in arteries
form a rigid arterial wall to withstand high blood pressure and can contract to narrow the lumen to increase pressure
elastic fibres in arteries
allow the arterial wall to stretch and expand upon the flow of a pulse and help maintain arterial pressure between pump cycles through elastic recoil.
- Elastic recoil helped because it pushes the blood forward through the artery and maintains pressure between pump cycles.
Function of capillaries
- exchange materials at low pressure
- Arteries split into arterioles which in turn split into capillaries, decreasing arterial pressure as total vessel volume is increased and the branching helps to ensure the slow movement
- Capillaries pool into venules which collate into larger veins after material exchange has occurred
Capillary structure and location
- wall may be continuous with endothelial cells held together by tight junctions to limit the permeability of large molecules or sinusoidal and have open spaces between cells and be permeable to large molecules and cells (e.g. in liver)
- tissues specialised for absorption (e.g. intestines, kidneys), the capillary wall may be fenestrated (contains pores)
low-pressure blood flow in capillaries is because…
allows for maximal material exchange
Hydrostatic pressure in the Capillaries
- higher hydrostatic pressure at the arteriole end of the capillary forces material from the bloodstream into the tissue fluid
- lower hydrostatic pressure at the venule end of the capillary allows materials from the tissues to enter the bloodstream
Veins
collect the blood from the tissues and convey it at low pressure to the atria of the heart.
- Have a large lumen to maximize flood flow
- They have a thin wall containing less muscle and elastic fibres as blood is flowing at a very low pressure
- Has more valves to prevent backflow as the pressure is low
How do skeletal muscle groups help to facilitate blood flow
- When the skeletal muscles contract, they squeeze the vein and cause the blood to flow from the site of compression
- Veins typically run parallel to arteries, and a similar effect can be caused by the rhythmic arterial bulge created by a pulse
Myogenic
signal for a heart beat is initiated by the heart muscle cells rather than the brain
electrical conduction of a heart beat
- The sinoatrial node sends out an electrical impulse that stimulates contraction of the myocardium (heart muscle tissue)
- This impulse directly causes the atria to contract and stimulates another node at the junction between the atrium and ventricle
- This second node – the atrioventricular node (AV node) – sends signals down the septum via a nerve bundle (Bundle of His)
- The Bundle of His innervates nerve fibres (Purkinje fibres) in the ventricular wall, causing ventricular contraction
Nerve Signalling
The pacemaker is under autonomic (involuntary) control from the brain, specifically the medulla oblongata (brain stem)
- Sympathetic nerve release noradrenaline = increase heart rate
- parasympathetic nerve release acetylcholine = decrease heart rate
Hormonal Signalling
chemical messengers released into the bloodstream that act specifically on distant target sites.
- in the heart adrenaline is released from adrenal glands which prepare for physical activity
Systole
Contraction
1. Blood returning to the heart will flow into the atria
2. atria will contract forcing blood into ventricles
3. ventricles contract, ventricular pressure exceeds atrial pressure and AV valves close to prevent backflow (first heart sound)
4. both sets of heart valves closed, pressure rapidly builds in the contracting ventricles
5. pressure exceeds blood pressure in the aorta, blood is released into the aorta
Diastole
Relaxation
1. as blood exits the ventricle and travels down the aorta, ventricular pressure falls
2. pressure drops below aortic pressure, the aortic valve closes to prevent backflow (second heart sound)
3. AV valve opens and blood can flow from atria to ventricle
4. aortic pressure remains quite high as muscle and elastic fibres in the artery wall maintain blood pressure
The first line of defence in our bodies
Surface barriers
- Skin - Secretes acid to lower PH and has biochemical defence agents
- Mucous Membranes - protected internal structures consisting of living surface cells that release fluids to wash away pathogens also have the same as skin
What are the two key components of a blood clot
- Platelets - when activated to form a sticky plug at the damaged region
- Fibrin strands - an insoluble mesh of fibres that trap blood cells at the site of damage
Coagulation Cascade
the process by which blood clots are formed involves a complex set of reactions collectively. Stimulated through clotting factors
Explain the coagulation cascade
- Clotting factor makes the platelets sticky so it sticks to the damaged region and forms a plug
- also initiate vasoconstriction to it reduced the blood flow
- clotting factors trigger the conversion into thrombin
- then thrombin triggers creation of fibrin
- fibrin creates a mesh to create a temporary clot
- once healed the enzyme plasmin dissolves the clot
Coronary Thrombosis
formation of a clot within the blood vessels that supply and sustain the heart tissue
- fatty deposits develop in arteries and reduce the diameter of the lumen leading to increase pressure and damage
What is the second line of defence
innate immune system
Phagocytes
White blood cells that engulf and digest foreign bodies (pathogens)
How do phagocytic leukocytes respond to infection?
Phagocytic leukocytes are drawn to the site of infection by chemicals released by damaged tissues (such as histamine) via a process called chemotaxis. and engulf the pathogen when cellular extensions (pseudopodia) surround the pathogen
What happens after a pathogen is engulfed during phagocytosis?
The vesicle is then fused to a lysosome, forming a phagolysosome, and the pathogen is digested.
What is the purpose of presenting pathogen fragments (antigens) on the surface of the phagocyte?
Pathogen fragments (antigens) may be presented on the surface of the phagocyte in order to stimulate the third line of defence.
The third line of defence
adaptive immune system, which is specific in its response. Lymphocytes
What are the two types of Lymphocytes
B cells - Antibody-producing cells that recognise and target particular pathogen fragments
Helper T cells - regulator cells that release chemicals to activate specific B cells
What happens when phagocytic leukocytes present antigen fragments on their surface?
- Antigen-presenting cells (dendritic cells) migrate to the lymph nodes and activate specific helper T lymphocytes.
- helper T cells then release cytokines to activate the particular B cell capable of producing antibodies specific to the antigen
- B cell will divide and differentiate to form short-lived plasma cells that produce high amounts of specific antibody
- Antibodies will target their specific antigen, enhancing the capacity of the immune system to recognize and destroy the pathogen
- Some b cells develop memory cells and provide long lasting immunity
Antigen
An antigen is a substance that the body recognises as foreign and that will elicit an immune response
Antibody:
Protein produced by b cells and is specific to a given antigen
Antibiotics
compounds that kill or inhibit the growth of microbes (specifically bacteria) by targeting prokaryotic metabolism.
However, virus cannot be treated through antibiotics as they need to be with specific antiviral agents (no metabolism)
Antibiotic resistance
Genes may confer resistance by encoding traits that degrade the antibiotic, block its entry, increase its removal or alter the target. (Natural Selection)
Penicillin
The medical applications of penicillin as an antibiotic were demonstrated
- Eight mice were injected with hemolytic streptococci and four of these mice were subsequently injected with doses of penicillin
- The untreated mice died of bacterial infection while those treated with penicillin all survived – demonstrating its antibiotic potential
Effects of HIV
- HIV specifically targets the helper T lymphocytes which regulate the adaptive immune system
- With a reduction in the number of helper T cells, antibodies are unable to be produced, resulting in a lowered immunity. Results in susceptibility to infection
Process involved in respiration
- Ventilation - exchange of air between the atmosphere and the lungs
- Gas exchange - exchange of oxygen and carbon dioxide between the alveoli and bloodstream
- Cell Respiration - The release of energy (ATP) from organic molecules – it is enhanced by the presence of oxygen
What is the purpose of ventilation
gas exchange is a passive process, a ventilation system is needed to maintain a concentration gradient in alveoli.
- O2 levels stay high in alveoli (and diffuse into the blood) and CO2 levels stay low (and diffuse from the blood)
Respiratory System
- Air enters the nose or mouth
- passes through the trachea until it divides into two bronchi
- right lung is composed of three lobes, while the left lung is only comprised of two
- bronchi divide into many smaller airways called bronchioles (increase SA)
- bronchiole terminates with a cluster of air sacs called alveoli, where gas exchange with the bloodstream occurs
Alveolus
Alveoli function as the site of gas exchange
- thin epithelial layer (one cell thick) to minimise diffusion distances for respiratory gases
- rich capillary network to increase the capacity for gas exchange with the blood
- roughly spherical in shape for SA
- the internal surface is covered with a layer of fluid, as dissolved gases are better able to diffuse into the bloodstream
Pneumocytes
cells that line the alveoli and comprise of the majority of the inner surface of the lungs
What are Type 1 Pneumocytes
- Type 1 Pneumocytes - involved in the process of gas exchange between the alveoli and the capillaries
- Flat and thin to minimising diffusion distance
- connected by occluding junctions, which prevents the leakage of tissue fluid
- amitotic and unable to replicate
What are Type 2 Pneumocytes
- responsible for the secretion of pulmonary surfactant, which reduces surface tension in the alveoli
- cuboidal in shape and possess many granules (for storing surfactant components)
- can differentiate into type I cells
What does moist lining do
- easy diffusion
- tendency to collapse
pulmonary surfactant
Reduces surface tension in the alveoli
- so there is equal pressure and then it can make sure it inflates at the same times and inflate at a faster rate
- without surfactant, it becomes hard to inflate and can more likely collapse
Inspiration
muscles responsible for inspiration are the diaphragm and external intercostals
- muscles contract and the diaphragm flattens to allow an increase in volume.
- External intercostals contract, pulling ribs upwards and outwards (expanding chest)
Expiration
muscles responsible for expiration are the abdominal muscles and internal intercostals
- Diaphragm muscles relax and the diaphragm curves upwards to reduce the volume
- Internal intercostal muscles contract, pulling ribs inwards and downwards (reducing the breadth of the chest)
neurons
specialised cells that function to transport electrical impulses in the nervous system
Dendrites
branched fibres that convert chemical information into electrical signals
Axon
elongated fibre transmit electrical signals for communication with other neurons and effectors
Soma
cell body containing nucleus and organelles where metabolism occurs
what do myelin sheath do
insulating layer that increases speech of electrical impulses
how do neurons generate electrical signals
pump positively charged ions like (Na & K) across the membrane as unequal distribution of ions on different sides creates membrane potential
Resting potential
The difference in charge when a neuron is not firing between two sides of a membranes
How to maintain resting potential
It is controlled by sodium-potassium pumps
1. pump will expel 3 Na ions and 2 K ions
2. Electrochemical gradient created where the interior is more negative than the exterior (more pos ions outside less inside)
3. And ATP is required for this exchange
Action potential
rapid changes in charge across the membrane that occur when a neuron is firing
What are the main stages of the action potential?
Depolarization
Repolarization
Refractory period
Depolarization
The sudden change from a negative to a positive internal charge
1. sodium channel open in axon
2. Lots of Na+ outside will passively flow inside
3. causes the membrane potential to become positive
Repolarisation
Restore membrane potential after depolarisation
1. Potassium channels open in axon
2. Lots of K+ on the inside so passively move outside
3. Causes membrane potential to return to a negative internal differential
Refractory Period
period of time following a nerve impulse before the neuron fires again
1. Normal resting state is when Na is outside and K is inside
2. after de and re polarization ionic distribution is reversed
3. before the neuron fires again resting potential is restored by antiports of sodium-potassium pumps
Nerve impulses
action potential that moves along the length of the axon as a wave of depolarization
1. ion channels that are on axon only open in response to changes in membrane potential (Voltage gated)
2. therefor depolarization at one point triggers the next segment to open
all or none principle
action potential of the same magnitude will always occur if a minimum electrical stimulus is generated (to open voltage-gated channels)
if the threshold potential is not reached, no action potential and hence the neuron will not fire
unmyelinated neurons
action potentials propagate sequentially along the axon in a continuous wave of depolarisation
myelinated neurons
action potentials ‘hop’ between the gaps in the myelin sheath called the nodes of Ranvier
disadvantage of Myelination
takes up significant space within an enclosed environment
What are synapses
The physical gaps that separate neurons from other cells
What are the steps on chemical Transfer across synapses
- Action potential reaches axon terminals voltage gated calcium channels open
- Ca+ diffuses into the cell and promote the fusion of vesicles that normally contain neurotransmitters
- Neurotransmitter released via exocytosis across synaptic cleft
- Neurotransmitters bind to specific receptors on the post-synaptic membrane and open ligand-gated ion channels
- opening of ion channels generates an electrical impulse will cause signals
- Neurotransmitters are then recycles via uptake pumps or degraded
What can neurotransmitters do
Trigger (excitatory) or prevent (inhibitory) response
What is acetylcholine
- neurotransmitter that binds to receptor on muscle fibers to trigger muscle contraction
- promote parasympathetic responses (‘rest and digest’)
Is acetylcholine constantly removed? Why?
Yes. as overstimulation can lead to conclusions or paralysis
How is acetylcholine removed?
acetylcholinesterase breaks acetylcholine down into choline where it is then transported back to make more.
What are Neonicotinoid pesticides?
hey are able to bond to nicotinic acetylcholine receptors irreversibly and due too it not being able to be broken down it can cause permanent overstimulation
What do low activation of acetylcholine receptors promote?
Nerve signaling
Why does Neonicotinoid work as good pesticide?
In insects it binds more strongly and therefor is more toxic
Graded potentials
Change in membrane potential when neurotransmitters bind to neuroreceptors on the post-synapticmembrane of target cells and open ligand-gated ion channels
When is a nerve impulse initiated?
Threshold is reached so voltage-gated ion channels open
What causes depolarisation? Why?
Excitatory neurotransmitters are able to open ligan-gated channels (sodium or calcium)
What causes hyperpolarisation? Why?
nhibitory neurotransmitters open ligan-gated channels (potassium or chlorine)
