General Principles Week 2 Flashcards
TLO 1.1: Gametogenesis Comparison
Spermatogenesis:
Continuous in males from puberty.
Produces four functional spermatids from one primary spermatocyte.
Takes ~64 days to complete.
Results in small, motile gametes.
Spermatogenesis is the process of producing sperm cells in males. It happens in the testes and involves several steps:
1. Formation of Sperm Cells: It starts with spermatogonia (stem cells), which divide to form immature sperm cells.
2. Meiosis: These immature cells undergo meiosis, a type of cell division that reduces the chromosome number by half, creating four haploid sperm cells.
3. Maturation: The haploid cells mature into fully functional sperm, gaining a tail for swimming and a head containing genetic material.
Spermatogenesis ensures that sperm are ready for reproduction, carrying half the genetic information needed to form an offspring.
TLO 1.1: Gametogenesis Comparison
Oogenesis:
Oogenesis is the process of creating an egg, or ovum, in a female fetus. It starts in the ovaries around seven weeks into gestation.
Process
Primordial germ cells: In the female fetus, primordial germ cells (PGCs) colonize the ovaries.
Mitosis: PGCs undergo mitosis to become oogonia.
Oogonia become primary oocytes: Oogonia undergo maturation to become primary oocytes.
Meiosis: Primary oocytes undergo meiosis, which separates paired chromosomes and chromatids. This results in a secondary oocyte, which will complete meiosis if fertilized.
Ovulation: The secondary oocyte is released from the ovary during ovulation
TLO 1.2: Meiosis and Genetic Variability
Mechanisms for Variability:
Meiosis generates genetic variability primarily through two mechanisms:
crossing over (genetic recombination) which occurs during prophase I, and
independent assortment of chromosomes during metaphase I,
where homologous chromosomes randomly align, leading to diverse combinations of alleles in the resulting gametes
Independent assortment: Random alignment of chromosomes during metaphase I.
Crossing over: Exchange of genetic material during prophase I.
Random fertilization: Fusion of genetically diverse gametes.
TLO 1.2: Meiosis and Genetic Variability
Significance:
Promotes adaptation, disease resistance, and species evolution.
TLO 1.3: Fertilization and Zygotic Cleavage
Fertilization:
Fertilization is the process where a sperm cell penetrates an ovum (egg), essentially merging their genetic material to create a zygote, which marks the beginning of a new individual’s development; in simpler terms, it is when a sperm “penetrates the egg.
Sperm penetrates the ovum.
Pronuclei fuse to restore diploid chromosome number.
Cortical reaction prevents polyspermy.
Calcium triggers completion of meiosis II in the ovum.
TLO 1.3: Fertilization and Zygotic Cleavage
Zygotic Cleavage:
Zygotic cleavage is the process of cell division that occurs after fertilization to create a multicellular embryo. It is a series of mitotic divisions that produce smaller cells called blastomeres
Zygotic cleavage is the series of rapid cell divisions that occur after a zygote (fertilized egg) is formed. During this process:
1. Zygote to Blastomeres: The single-celled zygote divides into smaller cells called blastomeres without increasing in overall size.
2. No Growth Phase: The cleavage divisions lack a growth phase, meaning the total volume of the embryo remains the same while the cells become progressively smaller.
3. Formation of a Multicellular Structure: This process eventually forms a solid ball of cells (morula) or a hollow structure (blastula), depending on the organism.
Zygotic cleavage lays the foundation for the later stages of embryonic development by creating the cells that will differentiate into tissues and organs.
TLO 1.4: Blastogenesis and Endometrial Implantation
Blastogenesis:
“Blastogenesis” refers to the early stage of embryonic development where a fertilized egg (zygote) divides rapidly to form a blastocyst, characterized by the formation of a fluid-filled cavity called the blastocoel, with an inner cell mass (which will become the embryo) surrounded by an outer layer of cells called the trophoblast (which will develop into the placenta)
Morula compacts and forms a blastocoel.
Blastocyst develops (inner cell mass + trophoblast).
TLO 1.4: Blastogenesis and Endometrial Implantation
Implantation:
“Implantation” refers to the process where a blastocyst, a ball of cells developed from a fertilized egg, attaches to and burrows into the lining of the uterus (endometrium), marking the initial stage of pregnancy; essentially, it’s the moment the embryo becomes embedded in the uterine wall and starts to develop further.
Blastocyst hatches from the zona pellucida.
Trophoblast attaches to and invades the endometrium.
Syncytiotrophoblast completes implantation (day 11–12 post-fertilization).
TLO 1.4: Blastogenesis and Endometrial Implantation
Consequences of Failure:
Sign of failed implantation. Cramping and spotting after a failed implantation is your body expelling the embryo after it failed to attach to the uterine wall
When implantation does not occur, a timely destruction of the fully developed endometrium leads to menstruation.
Recurrent implantation failure (~10% in IVF).
Causes: Immunological, thrombophilias, or embryo aneuploidy.
TLO 1.5: Germ Layers and Tissue Formation
Ectoderm
Mesoderm
Endoderm
The three germ layers, ectoderm, mesoderm, and endoderm, are the primary cell layers that develop early in an embryo and give rise to all the different tissues and organs in the body; with the ectoderm forming the skin and nervous system, the mesoderm forming muscles, bones, and connective tissue, and the endoderm forming the lining of the digestive and respiratory systems.
Breakdown:
Ectoderm (Outer Layer):
Develops into the epidermis (outer layer of skin), hair, nails, brain, spinal cord, and neural tissue.
Mesoderm (Middle Layer):
Develops into skeletal muscles, bones, cartilage, blood vessels, kidneys, and the reproductive organs.
Endoderm (Inner Layer):
Develops into the lining of the digestive tract, lungs, liver, pancreas, and other internal organs associated with the digestive system.
Topic 2: Epithelial Tissue
TLO 2.1: Embryonic Origin
Originates from:
Ectoderm
Mesoderm
Endoderm
Serosal membranes
Ectoderm: Epidermis, sweat glands.
Mesoderm: Kidney tubules, gonads.
Endoderm: Gastrointestinal and respiratory tract lining.
Serosal membranes: Primarily mesodermal origin.
TLO 2.2: Serosal Membranes
Location:
Composition:
Function:
Examples:
TLO 2.2: Serosal Membranes
Location: Line cavities and cover organs.
Composition: Simple squamous epithelium + connective tissue.
Function:
Reduce friction.
Produce lubricating fluid.
Compartmentalize body cavities.
Examples: Pleura, pericardium, peritoneum.
Serous membranes line body cavities and cover organs in those cavities. They are made up of two layers of mesothelial cells and secrete a thin, watery fluid called serous fluid. Serous membranes reduce friction between organs and the walls of the body cavity.
Location Serous membranes line the following cavities:
Thoracic cavity: The pleura lines the thoracic cavity and covers the lungs
Abdominal cavity: The peritoneum lines the abdominal cavity and covers the abdominal organs
Pericardial cavity: The pericardium surrounds the heart
Vaginal cavity: The tunica vaginalis surrounds the testes in males
Composition Serous membranes are made up of two layers of mesothelial cells. The visceral layer covers the organ, while the parietal layer covers the cavity wall.
Function Serous membranes reduce friction between organs and the walls of the body cavity. They also provide structural support and act as a protective barrier.
TLO 2.3: Epithelial Tissue Types
Simple squamous
Simple cuboidal
Simple columnar
Stratified squamous
Stratified cuboidal
Stratified columnar
Pseudostratified columnar
TLO 2.3: Epithelial Tissue Types
Simple squamous: Lines blood vessels and body cavities, and regulates the passage of substances
Simple cuboidal: Found in kidney tubules and glandular tissue, and secretes and absorbs substances
Simple columnar: Lines the stomach and intestines, and absorbs and secretes substances
Stratified squamous: Protects the body from microorganisms and water loss, and is the main component of the skin
**Stratified cuboidal: **Found in the excretory ducts of sweat and salivary glands
**Stratified columnar: **Found in the conjunctiva of the eyelids, and protects and secretes mucus
**Pseudostratified columnar: **Found in the trachea and upper respiratory tract, and secretes mucus
Simple squamous: Diffusion/filtration (e.g., alveoli).
Simple cuboidal: Secretion/absorption (e.g., kidney tubules).
Simple columnar: Absorption/secretion (e.g., intestinal lining).
Stratified squamous: Protection (e.g., esophagus).
Stratified cuboidal: Protection/secretion (e.g., sweat glands).
Stratified columnar: Protection/secretion (e.g., male urethra).
Pseudostratified columnar: Secretion/cilia action (e.g., respiratory tract).
TLO 2.4: Histological Identification
Based on:
Cell shape
Layers
Specialized structures
TLO 2.4: Histological Identification
Based on:
Cell shape (squamous, cuboidal, columnar).
Layers (simple, stratified).
Specialized structures (cilia, microvilli).
Cell shape
Squamous: Flat shape, with a width greater than its height
Cuboidal: Cube shape, with a width and height that are roughly equal
Columnar: Column shape, with a width smaller than its height
Layers
Simple: One layer of cells
Stratified: Two or more layers of cells
Pseudostratified: Appears to be stratified, but is actually one layer of cells
TLO 2.5: Cell Junctions
Tight junctions
Adherens junctions
Desmosomes
Gap junctions
TLO 2.5: Cell Junctions
Tight junctions: Seal adjacent cells (e.g., blood-brain barrier).
Adherens junctions: Anchor cells (e.g., epithelial sheets).
Desmosomes: Strong adhesion (e.g., skin epidermis).
Gap junctions: Cell communication (e.g., cardiac muscle).
Tight junctions:
Create a watertight seal between cells, preventing leakage of fluids and molecules between them, essentially acting as a barrier function; often found in epithelial tissues like the lining of the bladder or stomach.
Adherens junctions:
Anchor cells to each other by connecting to the actin cytoskeleton, providing structural support and allowing for cell-to-cell adhesion; involved in cell migration and tissue development.
Desmosomes:
Strong, spot-like junctions that connect the intermediate filaments of neighboring cells, providing strong mechanical stability and resisting shearing forces; commonly found in tissues experiencing high stress like skin.
Gap junctions:
Form channels between cells allowing for direct communication and passage of small molecules like ions, enabling rapid electrical signaling between cells
TLO 2.6: Glandular Tissue
Exocrine glands:
Simple:
Compound:
Endocrine glands:
TLO 2.6: Glandular Tissue
Exocrine glands:
Simple: Single duct (e.g., sweat glands).
Compound: Branched ducts (e.g., salivary glands).
Endocrine glands:
Secrete directly into bloodstream (e.g., thyroid).
Exocrine glands secrete substances through ducts onto the body’s surfaces, while endocrine glands secrete substances directly into the bloodstream. The pancreas is an organ that contains both exocrine and endocrine glands.
Exocrine glands
Pancreas: Secretes digestive enzymes into the duodenum, such as trypsinogen and chymotrypsinogen. The pancreas also secretes bicarbonate ions to neutralize acidic chyme.
Sweat glands: Secrete sweat onto the body’s surface
Lacrimal glands: Secrete tears onto the body’s surface
Salivary glands: Secrete saliva onto the body’s surface
Mammary glands: Secrete milk onto the body’s surface
Endocrine glands
Pituitary gland: Located in the brain, this gland secretes hormones that regulate metabolism, mood, and sexual reproduction.
Thyroid gland: An endocrine gland that secretes hormones.
Adrenal glands: Located on top of each kidney, these glands secrete hormones that regulate metabolism, blood pressure, and the body’s stress response.
Pineal gland: Located at the base of the brain, this gland secretes melatonin, which helps regulate sleep and circadian rhythms.
Parathyroid glands: Located in the neck, these glands regulate calcium levels in the blood.
TLO 2.7: Exocrine Secretion Mechanisms
Merocrine:
Apocrine:
Holocrine:
TLO 2.7: Exocrine Secretion Mechanisms
Merocrine: Exocytosis (e.g., pancreatic enzymes).
Apocrine: Cytoplasm released with secretion (e.g., mammary glands).
Holocrine: Entire cell disintegrates (e.g., sebaceous glands).
The most damaging type of secretion to cells is holocrine, whereas merocrine is the least damaging, and apocrine is in between them. Note: -Endocrine glands are the glands that release their secretions directly into the blood and hence they are known as ductless glands.
Merocrine
The most common type of gland, merocrine glands release secretions through exocytosis. This process doesn’t damage the cell. Examples of merocrine glands include eccrine sweat glands, which are found in the palms of the hands and soles of the feet.
Apocrine
Apocrine glands release secretions by pinching off part of the cell membrane. This causes the cell to lose some of its cytoplasm. Examples of apocrine glands include mammary glands, which produce breast milk.
Holocrine
Holocrine glands release secretions by rupturing the cell membrane. This destroys the cell, causing the entire cell to become part of the secretion. Examples of holocrine glands include sebaceous glands, which produce sebum, an oily substance that lubricates the skin.
Topic 3: Connective Tissue
TLO 3.1: Embryonic Origin
Mesoderm:
Mesenchyme:
Hematopoietic stem cells:
Mesoderm: A layer of cells in the middle of an organism.
Mesenchyme: An embryonic connective tissue that comes from the mesoderm.
Hematopoietic stem cells: Cells that produce all the cells in the blood.
Mesoderm:
Mesenchyme: Fibroblasts, adipocytes.
Hematopoietic stem cells: Blood cells, immune cells.
TLO 3.2: Connective Tissue Cell Types
Fibroblasts:
Adipocytes:
Macrophages:
Mast cells:
Plasma cells:
Chondrocytes:
Osteoblasts/Osteocytes:
TLO 3.2: Connective Tissue Cell Types
Fibroblasts: ECM synthesis.
**Adipocytes: **Fat storage.
Macrophages: Phagocytosis.
**Mast cells: **Inflammatory mediators.
Plasma cells: Antibody production.
Chondrocytes: Cartilage matrix maintenance.
Osteoblasts/Osteocytes: Bone matrix maintenance.
1. Fibroblasts: These cells are essential for producing and maintaining the extracellular matrix, which provides structural support to tissues. They are especially involved in wound healing, creating collagen and other fibers.
**2. Adipocytes: **Also known as fat cells, adipocytes store energy in the form of fat. They play critical roles in metabolism, energy balance, and insulation. There are two types of adipocytes: white fat cells and brown fat cells.
**3. Macrophages: **These are key players in the immune system, responsible for detecting, engulfing, and destroying pathogens and dead cells. They also stimulate other immune cells and are involved in inflammation and tissue repair.
4. Mast Cells: Part of the immune system, mast cells play a pivotal role in* allergic reactions and inflammatory processes*. They release histamine and other chemicals during immune responses, contributing to inflammation.
5. Plasma Cells: These are mature B-lymphocytes that produce antibodies to fight against pathogens. They are an essential component of the adaptive immune system.
**6. Chondrocytes: **These cells are found in cartilage and are responsible for the synthesis and maintenance of cartilage matrix. They help maintain the structural integrity of cartilage tissue.
7. Osteoblasts/Osteocytes: Osteoblasts are cells that form new bone, synthesizing and secreting the bone matrix. Once they become embedded in the matrix they create, they differentiate into osteocytes. Osteocytes maintain bone tissue and are crucial for bone health and remodeling.
Topic 4: Skeletal Tissue
TLO 4.1: Bone Cell Types
Osteoblasts:
Osteocytes:
Osteoclasts:
Bone lining cells:
Topic 4: Skeletal Tissue
TLO 4.1: Bone Cell Types
Osteoblasts: Bone-forming cells; synthesize and secrete bone matrix.
Osteocytes: Mature bone cells; maintain bone tissue.
Osteoclasts: Bone-resorbing cells; break down bone matrix.
Bone lining cells: Inactive osteoblasts covering bone surfaces.
Osteoblasts Create new bone by secreting collagen and other proteins that bind to calcium and phosphate from the bloodstream.
Osteocytes Mature osteoblasts that maintain bone structure by regulating mineral concentration. They are the most common cell in bone and can live as long as the organism.
Osteoclasts Large cells that break down bone by dissolving minerals and collagen. They are found at the surface of bone where resorption is occurring.
Bone lining cells Protect bone surfaces from osteoclast activity when bone is not being remodeled. They also regulate the movement of minerals in and out of bone.
TLO 4.2: Bone Tissue Organization
Compact bone:
Spongy bone:
Periosteum:
Endosteum:
TLO 4.2: Bone Tissue Organization
Compact bone: Dense, organized with osteons (Haversian systems).
Spongy bone: Porous with trabeculae.
Periosteum: Outer fibrous layer covering bones.
Endosteum: Inner membrane lining bone cavities.
Compact bone
The dense, rigid outer layer of bone. It’s made up of osteons, which are microscopic units of calcified matrix.
Spongy bone
The lighter, less dense inner layer of bone. It’s made up of trabeculae and contains red bone marrow, which produces blood cells.
Periosteum
The tough, shiny membrane that covers the outer surface of most bones. It’s made of connective tissue and bone-forming cells, and helps bones grow, heal, and repair.
Endosteum
The delicate membrane that lines the cavities within bones, such as the medullary cavity.
TLO 4.3: Ossification Processes
Intramembranous ossification:
Intramembranous ossification is the process of creating bone tissue from connective tissue membranes. It’s a key part of fetal development and continues until a person is about 25 years old.
Intramembranous ossification: Intramembranous ossification: begins within fibrous connective tissue membranes formed by mesenchymal cells. Intramembranous ossification: Forms frontal, parietal, occipital, temporal, and clavicle bones.
Occurs in flat bones (e.g., skull, clavicle).
Mesenchymal cells differentiate directly into osteoblasts.
No cartilage intermediate.
TLO 4.3: Ossification Processes
Endochondral ossification:
Endochondral ossification is a process that replaces cartilage with bone during fetal development and bone growth. It’s one of the two main ways bone tissue is created in the mammalian skeletal system.
Occurs in long bones and vertebrae.
Cartilage model is replaced by bone.
Growth plates enable longitudinal growth.
TLO 4.3: Ossification Processes
Similarities:
Intramembranous and endochondral ossification are similar processes that both create bone tissue.
Similarities
Both processes produce bone tissue.
Both processes involve osteoblasts, which are cells that create bone.
Both processes occur before birth.
Differences
Intramembranous ossification: Forms bones from connective tissue, such as the skull.
Endochondral ossification: Forms bones from cartilage, such as long bones, short bones, and the ends of flat bones.
TLO 4.4: Common Bone Disorders
Osteoporosis:
Causes:
Osteomalacia/Rickets:
Causes:
Paget’s disease:
Causes:
Osteomyelitis:
Causes:
TLO 4.4: Common Bone Disorders
Osteoporosis
Bones become brittle and weak due to loss of bone density
Can be caused by aging, hormonal changes, and poor diet
Can be treated with medication or lifestyle changes
Rickets and osteomalacia
Bones become soft due to a lack of calcium or vitamin D
Can be caused by poor diet, lack of sunlight, or an inability to absorb vitamin D
Can be treated with vitamin supplements or a yearly vitamin D injection
Paget’s disease
Bones become misshapen due to excessive bone resorption and disorganized bone growth
Can affect the spine, pelvis, and skull
Can progress in the preexisting site, but does not spread to other bones
Other bone disorders include:
Osteogenesis imperfecta, which makes bones brittle
Renal osteodystrophy, which can be caused by kidney disease
Familial hypophosphatemia, a hereditary disorder that causes low levels of phosphate in the blood
Osteoporosis: Decreased bone density; increased fracture risk.
Causes: Age, hormonal changes, lack of exercise, poor nutrition.
Osteomalacia/Rickets: Inadequate mineralization.
Causes: Vitamin D deficiency, calcium or phosphate imbalance.
Paget’s disease: Abnormal remodelling.
Causes: Genetic factors, viral infections.
Osteomyelitis: Bone infection.
Causes: Bacterial/fungal infections via bloodstream or injury.
Topic 5: Blood
TLO 5.1: Major Components
Plasma:
Components:
Formed elements:
Includes:
The four main components of blood are plasma, red blood cells, white blood cells, and platelets.
Plasma
The liquid component of blood that carries blood cells throughout the body
Plasma is yellowish in color
Red blood cells
Also known as erythrocytes, these cells carry oxygen from the lungs to the body’s tissues
Red blood cells are the most common type of cell in blood
They are produced in bone marrow and have a diameter of about 6 micrometers
White blood cells
Also known as leukocytes, these cells help fight infections and disease
There are several types of white blood cells, including lymphocytes, monocytes, eosinophils, basophils, and neutrophils
Platelets
Also known as thrombocytes, these small, colorless cell fragments help stop bleeding
Platelets stick to the lining of blood vessels to help prevent or stop bleeding
Blood cells are produced in bone marrow, a spongy material in the center of bones.
Plasma: Liquid (55% of blood).
Components: Water, proteins, electrolytes, nutrients, hormones, waste.
Formed elements: Cellular (45% of blood).
Includes: Erythrocytes, leukocytes, platelets.
TLO 5.2: Blood Cell Types and Functions
Erythrocytes:
Leukocytes:
Neutrophils:
Lymphocytes:
Monocytes:
Eosinophils:
Basophils:
Platelets:
Erythrocytes, leukocytes, neutrophils, lymphocytes, monocytes, eosinophils, basophils, and platelets are all types of blood cells.
Erythrocytes
Also known as red blood cells (RBCs)
The most common type of blood cell
Carry oxygen from the lungs to the body’s tissues
Contain hemoglobin, a protein that carries oxygen
Leukocytes
Also known as white blood cells (WBCs)
Part of the immune system and help fight infection
Types of leukocytes include lymphocytes, monocytes, eosinophils, basophils, and neutrophils
Neutrophils
A type of white blood cell that helps heal damaged tissue and resolve infections
A lower than normal neutrophil count is called neutropenia
Lymphocytes
A type of white blood cell that helps the body make cells that fight infection and make antibodies
Part of the adaptive immune system
Monocytes
A type of white blood cell that helps other white blood cells remove damaged tissue and gobble up bacteria, viruses, debris, and infectious organisms
Eosinophils
A type of white blood cell that kills parasites, destroys cancer cells, and helps the immune system with an allergic response
Contain granules that contain antihistamine molecules and molecules toxic to parasitic worms
Basophils
A type of white blood cell that releases histamine if there is an allergic reaction and helps prevent blood clots
Platelets Also known as thrombocytes, Help in blood clotting, and A low number of platelets is called thrombocytopenia.
Erythrocytes: Oxygen transport; biconcave, no nucleus.
Leukocytes: Immune defense.
Neutrophils: Bacteria phagocytosis.
Lymphocytes: Adaptive immunity (T/B cells).
Monocytes: Phagocytosis, antigen presentation.
Eosinophils: Parasite defense, allergic response.
Basophils: Release inflammatory mediators.
Platelets: Blood clotting; derived from megakaryocytes.
TLO 5.3: Myeloid vs. Lymphoid Cell Lines
Myeloid:
Lymphoid:
TLO 5.3: Myeloid vs. Lymphoid Cell Lines
Myeloid cells give rise to various cells, including red blood cells, platelets, granulocytes (neutrophils, eosinophils, basophils), monocytes, and dendritic cells. Lymphoid cells produce lymphocytes, including B cells, T cells, and natural killer (NK)
Myeloid:
Includes: Erythrocytes, platelets, granulocytes, monocytes.
Shorter lifespan.
Lymphoid:
Includes: T/B lymphocytes, NK cells.
Primarily adaptive immunity.
TLO 5.4: Erythrocyte Dysfunction and Anemias
Iron deficiency anemia:
Vitamin B12 deficiency:
Sickle cell anemia:
Thalassemia:
Iron deficiency anemia, vitamin B12 deficiency, sickle cell anemia, and thalassemia are all types of anemia. Anemia is a blood disorder that occurs when your body doesn’t have enough healthy red blood cells.
**Iron deficiency anemia
**Occurs when your body doesn’t have enough iron to produce hemoglobin
Can be caused by poor diet or blood loss
Can be treated by eating iron-rich foods and foods rich in vitamin C
**Vitamin B12 deficiency anemia
**Occurs when your body doesn’t have enough vitamin B12
Can be caused by inadequate intake or absorption issues
Can be treated with vitamin B12 supplements, injections, or nose sprays
**Sickle cell anemia
**An inherited disease that can cause anemia
Thalassemia
An inherited disease that can cause anemia
Beta-thalassemia minor is often discovered during a routine blood count
**Other causes of anemia include:
**Folate deficiency, Chronic diseases, Infections, Certain medications, Bleeding, and Bone marrow problems.
**Symptoms of anemia include:
**Weakness
Dizziness
Shortness of breath
Headache
Pale or yellow skin
Chest pain
Iron deficiency anemia: Insufficient iron; microcytic, hypochromic.
Vitamin B12 deficiency: Impaired DNA synthesis; macrocytic, neurological symptoms.
Sickle cell anemia: Hemoglobin mutation; sickle-shaped cells, crises.
Thalassemia: Defects in globin chain production; microcytic anemia.
Topic 6: Muscular Tissue
TLO 6.1: Key Characteristics
Excitability
Contractility
Extensibility
Elasticity
Excitability:
When a muscle receives a signal from a nerve, it can respond by initiating a contraction.
Contractility:
This is the primary function of muscle tissue, where the muscle fibers shorten to generate force.
Extensibility:
Muscles can be stretched without tearing, allowing for flexibility in movement.
Elasticity:
After being stretched, a muscle can recoil back to its original length due to its elastic properties.
Excitability: Respond to stimuli.
Contractility: Shorten and generate force.
Extensibility: Stretch without damage.
Elasticity: Return to original length.
TLO 6.2: Muscle Cell Types
Smooth muscle:
Skeletal muscle:
Cardiac muscle:
TLO 6.2: Muscle Cell Types
Smooth muscle: Involuntary, non-striated (e.g., hollow organs, vessels).
Skeletal muscle: Voluntary, striated (e.g., attached to bones).
Cardiac muscle: Involuntary, striated (e.g., heart).
Smooth muscle:
Found in the walls of internal organs like the stomach, bladder, and blood vessels, responsible for involuntary movements like digestion and blood pressure regulation; appears smooth under a microscope due to lack of striations.
Skeletal muscle:
Attached to bones, responsible for voluntary movements like walking and lifting; appears striated under a microscope and is controlled by the somatic nervous system.
Cardiac muscle:
Located only in the heart, responsible for pumping blood throughout the body; appears striated like skeletal muscle, but is involuntary and controlled by the autonomic nervous system.
Key differences:
Control:
Smooth and cardiac muscles are involuntary, while skeletal muscle is voluntary.
Location:
Skeletal muscles are attached to bones, while smooth muscle is found in internal organs and cardiac muscle is only in the heart.
Appearance:
Both cardiac and skeletal muscle appear striated under a microscope, while smooth muscle does not.
TLO 6.3: Muscle Contraction (Sliding Filament Theory)
Sliding filament theory, a muscle fiber contracts when myosin filaments pull actin filaments closer together and thus shorten sarcomeres within a fiber. When all the sarcomeres in a muscle fiber shorten, the fiber contracts.
Calcium released from sarcoplasmic reticulum.
Calcium binds troponin; myosin binding sites exposed on actin.
Myosin binds actin (cross-bridge formation).
ATP hydrolysis powers the power stroke.
ATP binding causes myosin release.
Cycle continues until calcium is removed.
Topic 7: Nervous Tissue
TLO 7.1: Embryonic Origins
Neural tube:
Neural crest:
In embryonic development, the neural tube originates from the folding of the neural plate, a structure formed from the ectoderm, and eventually develops into the central nervous system (brain and spinal cord), while the neural crest arises from the borders of the neural plate, migrating away to form a diverse range of cell types including neurons of the peripheral nervous system, cartilage, bone, and pigment cells.
Key points about their origins:
Neural tube:
Forms from the neural plate which is a thickened region of the ectoderm.
Folds inwards to create a tube-like structure.
Eventually develops into the brain and spinal cord.
Neural crest:
Develops at the edges of the neural plate, between the neural plate and the non-neural ectoderm.
Cells “delaminate” from the neural tube and migrate extensively throughout the embryo.
Differentiates into a wide variety of cell types depending on their migration pathway.
Neural tube: Forms CNS (brain, spinal cord).
Neural crest: Forms PNS and some CNS components.
TLO 7.2: Cellular Components
Neurons:
Glial cells:
Astrocytes:
Oligodendrocytes:
Microglia:
Ependymal cells:
Schwann cells:
Neurons
Neurons are divided into four types: unipolar, bipolar, multipolar, and pseudounipolar.
Neurons require help from glial cells to form strong connections and eliminate obsolete connections.
Glial cells
Glial cells are the most abundant cells in the central nervous system.
Glial cells help maintain homeostasis and form myelin.
Glial cells are classified by their morphology, location, function, and molecular composition.
Types of glial cells
Oligodendrocytes: Form the myelin sheath around axons in the central nervous system
Schwann cells: Form the myelin sheath around axons in the peripheral nervous system
Astrocytes: Provide nutrients, structural support, and maintain the extracellular environment of neurons
Microglia: Scavenge pathogens and dead cells
Ependymal cells: Produce cerebrospinal fluid that cushions neurons
Satellite cells: Provide nutrients and structural support to neurons in the peripheral nervous system
Radial glia: Involved in neurogenesis and neural development
Neurons: Transmit signals.
Glial cells:
Astrocytes: Support neurons; maintain blood-brain barrier.
Oligodendrocytes: Myelinate CNS axons.
Microglia: Immune defense.
Ependymal cells: Line ventricles; produce cerebrospinal fluid.
Schwann cells: Myelinate PNS axons.
TLO 7.3: Neural Cell Structures
Soma
Dendrites
Axon
Myelin sheath
Nodes of Ranvier
Soma:
This is the central part of a neuron, containing the nucleus and other organelles, essentially the “brain” of the cell where most cellular processes occur.
Dendrites:
These are short, branching extensions that extend from the soma and receive incoming signals from other neurons, acting like the “antennae” of the neuron.
Axon:
A long, thin fiber that carries electrical impulses away from the cell body to other neurons, muscles, or glands.
Myelin sheath:
A fatty layer that wraps around the axon, acting as an insulator to speed up signal transmission by allowing for “saltatory conduction” where the signal jumps between gaps in the myelin.
Nodes of Ranvier:
These are the gaps in the myelin sheath where the axon membrane is exposed, allowing for the signal to be regenerated and rapidly jump along the axon.
Soma: Signal integration.
Dendrites: Receive signals.
Axon: Conducts action potentials.
Myelin sheath: Insulates axons; speeds conduction.
Nodes of Ranvier: Gaps in myelin; enable saltatory conduction.
TLO 7.4: Myelin in CNS vs. PNS
CNS central nervous system:
PNS peripheral nervous system:
TLO 7.4: Myelin in CNS vs. PNS
CNS: Myelinated by oligodendrocytes; limited regeneration.
PNS: Myelinated by Schwann cells; better regeneration.
CNS: Includes only the brain and spinal cord.
PNS: Contains all nerves that extend from the brain and spinal cord to the body’s extremities.
Topic 8: Anatomical Position, Planes, and Terminology
TLO 8.1: Anatomical Position
Topic 8: Anatomical Position, Planes, and Terminology
TLO 8.1: Anatomical Position
Upright, face forward, arms at sides, palms forward, feet together.
TLO 8.2: Clinical Importance
Topic 8: Anatomical Position, Planes, and Terminology
Standardizes descriptions.
Aids in diagnosis, surgical planning, and imaging.
Anatomical position
Anterior: Toward the front of the body
Posterior: Toward the back of the body
Proximal: Close to the attachment point or trunk
Distal: Away from the attachment point or trunk
Superficial: Close to the surface of the skin
Deep: Away from the surface of the skin
Anatomical planes
Coronal plane: Separates the front and back of the body
Sagittal plane: Separates the left and right sides of the body
Transverse plane: Separates the upper and lower halves of the body
Anatomical terminology
Abdominopelvic cavity: The largest cavity in the body, which contains the digestive organs, kidneys, and adrenal glands
Pelvic cavity: Contains the rectum and most of the urogenital system
Cranial: A term used to refer to the skull
Cephalic: A term used to refer to the skull
Rostral: A term used to refer to the front of the face
Caudal: A term used in embryology and occasionally in human anatomy
TLO 8.3: Anatomical Planes
Sagittal:
Coronal:
Transverse:
Sagittal: Left/right.
Coronal: Front/back.
Transverse: Top/bottom.
TLO 8.4: Terminology
Directional:
Regional:
Cavities:
Movements:
TLO 8.4: Terminology
Directional: Superior, inferior, anterior, posterior, medial, lateral, proximal, distal.
Regional: Cephalic, thoracic, abdominal, pelvic.
Cavities: Dorsal (brain/spinal cord), ventral (thoracic, abdominopelvic).
Movements: Flexion, extension, abduction, adduction, rotation, pronation, supination.
Directional terms
Superior: Toward the head, or upper
Inferior: Away from the head, or lower
Anterior: Front
Posterior: Back
Medial: Toward the midline of the body
Lateral: Away from the midline of the body
Proximal: Closer to the trunk or point of attachment
Distal: Farther from the trunk or point of attachment
Superficial: Closer to the surface of the body
Deep: Farther from the surface of the body
Regional terms
The abdominopelvic cavity can be divided into regions or quadrants to describe the location of pain or masses
Cavities
Dorsal cavity
The cavity in the back of the body that contains the cranial and vertebral cavities
Ventral cavity
The cavity in the front of the body that contains the thoracic and abdominopelvic cavities
Thoracic cavity
The cavity within the rib cage that contains the heart and lungs
Abdominopelvic cavity
The largest cavity in the body that contains the digestive and reproductive organs
