Term 1 Learning Objectives Flashcards
Explain the difference between anatomy and physiology.
Anatomy → structure of the body (at gross and fine (i.e., histologic) scales)
Physiology → study of function (i.e, how the dynamic processes of the body occur)
These are linked concepts; neither makes sense without the other!
Use biological examples to illustrate key concepts in anatomy and physiology: structure/function, homeostasis, allostasis, and feedback.
- Structure determines function (e.g., space between bones indicates presence of muscles, tendons, ligaments and therefore motility)
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Homeostasis → ability to maintain a stable internal environment.
- Requires a sensor/receptor to detect the change, a control centre to integrate the information, and an effector to ‘fix’ the problem)
- Allostasis → ability to adapt the set point (or behaviour) to meet different conditions (e.g., blood pressure set point changes based on activity; carb-loading by marathon runners = behavioural allostasis)
- Negative feedback loops → buffer changes - return variable to set point (e.g., blood glucose levels)
- Positive feedback loops → amplify changes - each cycle moves system further from initial stable point (e.g., blood clotting)
Describe how curious features of our biology make (more) sense when considering development and evolution.
Bodies are products of development and evolution, both continuous processes.
For example, belly buttons only make sense if we consider development through time.
The recurrent laryngeal nerve is too long and only makes sense through consideration of the position of the larynx in modern and ancestral amphibians.
Evolution proceeds via natural and sexual selection, but it occurs within developmental constraints.
Explain why the chemistry of water and of carbon are critical for biology using examples.
Water is the most important substance in the body because:
- Water exists in different physical states at appropriate temperatures.
- Lubrication → water reduces friction within joints and in body cavities, preventing injury
- High heat capacity → helps maintain homeostasis
- Solvent → water can dissolve many substances
- Reactant and reaction medium → water is an ideal medium for biochemical reactions and sometimes participates as a reactant.
- High surface tension → due to hydrogen-bonding between individual water molecules.
Carbon (with hydrogen) is a component of every organic compound → key molecule for life because:
- Carbon can form four separate covalent bonds, enabling it to form rings, chains, and other extended structures.
- Functional groups added to a carbon skeleton introduce different properties to the molecule.
- Four types of carbon-containing (organic) molecules include:
- Carbohydrates
- Lipids
- Amino acids
- Nucleotides
Compare and contrast the different ways that molecules and ions can move across cell membranes.
- Diffusion of water across a selectively permeable membrane down its concentration gradient = osmosis.
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Passive processes (no ATP required):
- Diffusion
- Carrier-mediated transport (carrier or channel proteins like aquaporin = facilitated diffusion)
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Active processes require ATP:
- Vesicular transport → uses exocytosis or endocytosis to move molecules into/out of/ or through a cell
- Primary carrier-mediated transport → uses energy from the decomposition of high energy compounds to move ions/molecules through ‘pump’ proteins against their concentration gradient.
- Secondary carrier-mediated transport → ATP is consumed to generate a chemical gradient down which the target molecule can move; however, the energy is not used to directly move the molecule
Describe how failure to regulate the cell life cycle can lead to tumours and cancers.
Cells, unless told otherwise, will continuously divide. A failure to tell a cell that they should remain in the ‘interphase stage’ (not dividing) would result in a cell that divides unchecked. Anytime a cell divides there is a possibility that they may acquire a mutation that disrupts their ability to control the rate of division (creating an abnormal cell) which is why cancer is most common in tissues where cell division happens rapidly and continuously (i.e., epithelium of the skin).
Benign neoplasms (a.k.a. tumour) → contained within one location and tend to grow slowly
Malignant neoplasms → grow rapidly and have the potential to invade and destroy nearby normal tissue, as well as spread throughout the body
Cancer occurs when neoplasms spread (= metastases)
Describe the concentrations of sodium, potassium, chloride, and calcium across a cell membrane.
- [Sodium] → always higher outside cells
- [Chloride] → always higher outside cells
- [Potassium] → higher inside cells
- [Calcium] → higher outside cells
Name the four main types of tissue and explain where in the body they are likely to be found.
The four main types of tissue are epithelial, connective, muscle, and nervous tissue.
- Epithelial → (1) Covers exposed surfaces, (2) lines internal passageways and chambers, and (3) forms secretory glands. Mucous membranes, integument (skin), surrounding organs. Will be found anywhere where a barrier to external space/environments are needed; for example, the skin creates a barrier between the environment that is external to the body versus that that is internal, and the surfaces of organs create barriers to environments that are external to the organs, for example the acidic environment of the abdominal cavity versus the internal space of the digestive organs.
- Connective → (1) Fills internal spaces, (2) provides structural support, and (3) stores energy. In tendons, ligaments, bones, blood, also ‘packing material’ of the body that is not an organ / muscle / nerve.
- Nervous → (1) Excitable tissue that (2) conducts electrical impulses, and (3) carries information. The nervous system is branching and reaches the majority of the body as it is what allows communication between different parts of the body, and also allows for the sensation of touch. Found in many places in the body including the integument, muscles, the brain and spinal cord, and organs.
- Muscle → (1) Excitable tissue that (2) contracts to produce movement and (3) includes skeletal muscle, cardiac muscle, and smooth muscle. It will be found in the arms, legs, abdomen, heart, amongst other places. Places where it wouldn’t be found would probably be the lumen of non-cardiac organs, and the epidermis.
Compare and contrast the structure and general functions of different types of epithelial tissue, including glands.
Single layered epithelia are found in protected areas, whereas stratified epithelia are found in areas that have high physical and/or chemical stress. Similarly, epithelia with a greater apical surface compared to the lateral surface are more likely to be found in more protected areas, whereas epithelia with a smaller apical surface than lateral surface are likely to be found in areas with high physical and/or chemical stress.
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Epithelial structure: There are three different shapes that epithelial tissue comes in: squamous, cuboidal, and columnar. Additionally, each shape can be either stratified (with multiple cell layers), simple (with only one cell layer), or pseudostratified which consists of closely packed cells which appear to be arranged in layers but all of which in fact are attached to the basement membrane.
- COLUMNAR: stratified or simple. can be found in the intestine; helps with absorption in the digestive, renal tracts; has cilia and microvilli.
- CUBOIDAL: stratified or simple; found in the salivary glands, where it is stratified, as well as the kidney and pancreas (these are all compound gland sites, as well); helps with secretion and absorption.
- SQUAMOUS: stratified or simple; found in the epidermis, where it is stratified; its form allows it to be tightly packed making a firm, linked barrier between outside and inside
- PSEUDOSTRATIFIED COLUMNAR: found in the respiratory tract / trachea and helps filter air coming in and out; it is also contains cilia on its apical layer.
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Gland structure: Glands can either be simple (one duct), or compound (more than one duct). Examples of simple ducts are sweat glands, gastral glands, uterine glands, intestinal crypts. Examples of compound ducts are salivary glands, and pancreatic glands. Compound glands are normally found where high volumes are secreted.
- Functions and types of glands:
- EXOCRINE → specialized cells or groups of cells that secrete substances that reach the epithelial apical surface. Examples include sweat glands which help maintain thermal homeostasis, and sebaceous glands which lubricate surfaces of the body and keep moisture in while also forming a barrier against foreign substances
- ENDOCRINE: secrete into the bloodstream and into the interstitial fluid. An example is the release of hormones within the body.
- MEROCRINE: a mechanism by which a gland releases substances to external surfaces by exocytosis without actually destroying the gland cell (e.g., salivary galnds secrete mucin in vesicles)
- APOCRINE: a mechanism of secretion whereby the gland releases chemicals to the external surface via the shedding of the apical surface and cytoplasm of the cell (e.g., milk production by mammary glands)
- HOLOCRINE: a mechanism of secretion whereby the gland releases chemicals via the bursting (i.e., destruction) of the cell (e.g., sebum production by sebaceous glands)
- GOBLET CELL: secretes mucin (forms mucous when mixed with water) to the internal passageways to protect internal epithelia; merocrine unicellular duct.
- Functions and types of glands:
Explain the basic definition of connective tissue and classify whether a tissue is a connective tissue or not based on a description.
Connective tissue is defined by the presence of extracellular protein fibres, and cells suspended within a ground substance. Types of connective tissue are diverse, but share the property of having relatively few cells that sit in or move through an extracellular matrix. All types of connective tissue are formed from mesenchyme, which is a loose embryonic tissue.
You can tell if something is or is not connective tissue based on a few descriptive factors. The obvious one is the relatively lower number of cells in connective tissue types; if you are looking at two microscopic images of tissue, connective tissue will be the one that has more ECF and fewer cells. Additionally, there will be a high number of protein fibres present in the matrix (either collagen, reticular, or elastic fibres).
Compare and contrast the structure and general functions of different types of connective tissue.
There are three main types of connective tissue:
- CONNECTIVE TISSUE PROPER → tissue that has many types of cells and proteins. Either LOOSE, which creates a loose, open framework (reticular, adipose, or areolar), or DENSE where fibres are densely packed (elastic, regular, or irregular)
- FLUID → have distinctive cells that are suspended in a watery matrix with DISSOLVED proteins. Either BLOOD, which flows within the cardiovascular system, or LYMPH, which flows through the lymphatic system.
- SUPPORTIVE → has a LESS diverse cell population, and the matrix is much more densely packed (even more densely packed than dense connective tissue proper). Supportive tissue supports the placement of soft tissues / organs , holding things in place, and the position / weight of the body (skeletal system. It is made up of CARTILAGE which is a solid, rubbery matrix (includes hyaline, elastic, and fibro-cartilage), or BONE which is a solid, crystalline matrix.
How do connective tissue types COMPARE?
- All formed from mesenchyme, a loose and fluid embryonic tissue.
- All have an ECM, which is a nonliving substance made up of ground substance (flexible) and protein fibres which provide shape and structure.
- The presence of immature and mature cells of various types; -blasts. For example, fibroblasts, osteoblasts, and chondroblasts which are all immature, stem-type cells that secrete specific ground substances (chondroblasts for cartilage, osteoblasts for bone). The other end is the more mature cells, -cytes, like osteocyte, chondrocyte, etc, which maintain the health of the matrices which can sometimes revert back to their immature state if needed to create new ECM.
- The presence of macrophages
How do connective tissue types CONTRAST?
- Level of vascularization: for example, cartilage is avascular, whereas the dermis underlying the epidermis is heavily vascularized.
- Types of protein fibres vary in density and type
- The actual TYPES of immature and mature cells that create and maintain the ECM, as well as the types of fibres, and the amount of ground substance.
- Functions of the different types of connective tissue; supportive connective tissue in the form of bones supports the body weight, whereas loose adipose tissue provides padding and energy storage.
Explain the difference between a tissue membrane and a fascia.
On the most basic level, membranes are physical barriers, and fasciae create internal compartments and divisions. That may sound quite similar in terms of function, but the two differ in both form and function.
- MEMBRANES are always formed from epithelial tissue + connective tissue, specifically areolar tissue (structure). They line or cover body surfaces to provide BARRIERS, which facilitate absorption, reduce friction, and provide protection from external environments (function)
- FASCIAE are connective tissue layers that are made up of connective tissue only. There are three types of fasciae; superficial (areolar and adipose), deep (dense irregular), and subserous (areolar) (structure). Fasciae does not facilitate absorption, but rather exists as a supportive packing material to create compartments when needed for structural purposes, or to provide form so that organs are held in place (other connective tissue types do this too) (function).
Predict the consequences to the whole organism of a disruption of collagen synthesis.
Collagen aids in wound repair, dermis integrity, bone growth, bone matrix, outermost layers of blood vessels, amongst other functions in the body. Needless to say, it would be a big blow to the entire system if collagen synthesis was disrupted. Here are a few consequences that would occur:
- Skin thinning and dehydration; fine lines and wrinkles occur, elasticity of skin decreased (sagging), because collagen is the fibre that maintains much of the skin and provides its form
- Wounds would be slower to heal if less collagen was being synthesized, as collagen both triggers fibroblasts to the site of injury and also restores collagen to promote full skin regrowth and return the skin to its pre-wound rigidity and suppleness.
- Lots of other structures would also become weak, such as blood vessels and bones. The weakening would result from these structures having less connective tissue (in the form of collagen), which would reduce both their density and rigidity, make them more prone to breaks, etc.
To sum: collagen is important component of all sorts of connective tissues, so tissue would be prone to bruising as well. Barriers formed by epithelial and connective tissues could not be maintained due to lack of collagen production, so you would also be prone to infection because microorganisms could much more easily invade cells. Finally, the body would be a lot weaker due to loss of connective tissue holding muscles and joints together.
Not all connective tissues have the same functions. Give examples of varying functions of connective tissues.
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Establish a structural framework for the body
- Cartilage (flexible scaffolding)
- Reticular (a web of tissue that supports soft organs)
- Adipose (padding)
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Transport fluids and dissolved materials
- Red blood cells and lymph
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Protect delicate organs
- Reticular
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Support, surround, and interconnect other types of tissue
- Reticular
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Store energy, especially in the form of triglycerides
- Adipose
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Defend the body from invading microorganisms
- White blood cells
Explain at least four major functions of the integument and how these relate to the properties of the dermis, epidermis, and accessory structures.
Four major functions of the integument include: (1) regulation of thermal homeostasis, (2) providing a barrier against bacteria, viruses, and damage from the external environment, (3) fluid retention, and (4) the sensation of feeling.
- REGULATION OF THERMAL HOMEOSTASIS → relates to the eccrine and apocrine glands, which are accessory structures that begin in the dermis and move through the epidermis to release sweat to the external surface of the body. These glands promote evaporative cooling which helps regulate thermal homeostasis, however can also lead to dehydration in environmental conditions of heat with little access to water consumption. Additionally, hair follicles are an accessory structure that provide several functions including insulation.
- BARRIER AGAINST DAMAGE FROM EXTERNAL ENVIRONMENT → the stratified squamous epithelium that makes up the epidermis is tightly linked so it lets very little into the internal space of the body. The vascularization of the dermis allows for a quick response to any cuts or tears to the integument; the integument utilizes properties of fluid connective tissue (blood) such as the presence of macrophages to remove debris and other cells to prevent bacterial infection, as well as scab formation from blood platelets.
- FLUID RETENTION → the structure of the epithelial cells in the epidermis (squamous stratified) are tightly linked which prevents water from getting in or out, thereby keeping fluid inside your body. Additionally, sebaceous glands that release oil onto the surface of the skin and hair can provide a secondary barrier to keep fluid in, sort of like putting vaseline on something; it’s hard for water to move through it and evaporate.
- SENSATION OF FEELING → you are able to feel and sense your surroundings by touch / vibration from the external environment onto your skin. It is the part of your body that directly interacts with the external environment; thus, it is your gateway to the sensation of touch/feeling. This is supported in the integument by the innervation of the dermis; there are nerve endings throughout the dermis which respond to pressure and vibration and transport that sensory information to the brain, where it is communicated as sensation and a gateway to making sense of one’s environment.
Explain the function of melanin and how melanocytes contribute to skin colour.
Melanin is a pigment that produces a darker skin tone (relative to baseline skin tone), and which is very important in protecting skin cells (keratinocytes) from sun damage. Under normal circumstances, sunlight has two important effects on skin cells: (1) it allows for the synthesis of Vitamin D (2) it can lead to damage to the DNA of the cell, which over time increases the likelihood of mutations that lead to uncontrolled cell division, resulting in neoplasms / cancer. This damage occurs because the UV photons are absorbed by DNA, which puts DNA into a higher, more reactive energy state, which is unable to be released safely and instead results in reactions with water and other DNA molecules (= damage). Contrastingly, when a skin cell is melanized it also absorbs UV photons from the sun, but it is able to SAFELY handle that energy by omitting it as heat. The downside of melanization is that it prevents the skin cell from absorbing and synthesizing vitamin D from the sun, which can lead to bodily consequences such as Rickets (not so much anymore, because vitamin D can be absorbed from food, and foods are now supplemented with Vitamin D).
Melanin gets into the cell this way → melanocytes in the dermis transfer portions of their cytoplasm, known as melanosomes, to keratinocytes in the upper epidermis. Melanosomes are packed with melanin. People with darker skin have MORE active melanocytes that produce MORE melanosomes MORE frequently to the keratinocytes. Additionally, different skin tones arise from different forms of the same pigment; people of Asian ancestry will have a different form of melanin than those from African history.
Compare and contrast the processes of tissue repair in the dermis and epidermis.
DERMIS: repairs more slowly than epidermis, because it is forming new granulation tissue. Granulation tissue is a mixture of dividing mesenchymal cells, fibroblasts, and new blood vessels. Mast cell activation occurs in the dermis but not the epidermis; this is what results in the swelling around a new wound. Macrophages patrol the damaged areas, phagocytizing debris and pathogens. Extensive injuries result in the dermis repairing first. New capillaries form here
EPIDERMIS: repairs relatively more quickly via the proliferation of basal cells; the basal cells divide without daughter cells differentiating into keratinocytes, which allows for faster proliferation. The blood clot occurs here, restoring the integrity of the epidermis and restricting the entry of microorganisms in the area.
BOTH: Have a way to address pathogen and foreign body entrance to the body; dermis has macrophages, epidermis clots to form a scab and prevent entrance. Both dermis and epidermis are seeking to return skin to its pre-injury state, which is in a way homeostasis. Both responses involve the proliferation of cells in repair.
Explain how skin and UV exposure are linked to Vitamin D and calcium homeostasis.
- Calcium and vitamin D are linked together in that vitamin D is converted to a hormone in the kidneys (= calcitriol) that is critical for calcium absorption. While calcium is not directly absorbed from UV exposure, calcium homeostasis DOES rely on UV exposure (in the absence of dietary vitamin D) as it cannot be absorbed without the hormone produced via vitamin D absorption.
- UV is absorbed in the spinosum and basale layers of the epidermis in the keratinocytes. UV interacts with a protein in the keratinocytes which results in an active form of vitamin D.
Describe the effects of aging on the integument and analyze how this interacts with UV exposure.
Fewer melanocytes: melanocyte activity decreases and light skin people get very pale. When there’s less melanin in the skin, the integument becomes more sensitive to the UV rays because no melanin is present to absorb the harmful radiation. Sunburns are more likely. More UV absorption into the dermis = more DNA damage, DNA must be repaired, but DNA only has a limited amount of times it can repair itself successfully and accurately.
Thinning Epidermis: basal cell activity declines making skin thinner, which makes it more prone to injury and also decreases the skin’s metabolic abilities (it can’t make as much Vitamin D3 anymore)
Thinning Dermis: when the dermis thins it means there are less elastic fibres which weakens the structure of the integument causing wrinkles/sagging - most pronounced in areas that get the most sun
Compare and contrast the role of skin in thermal and osmotic homeostasis.
There is a trade off between thermal and osmotic homeostasis in the skin, particularly in conditions where the external environment is warm/hot. This trade off exists because one of the skin’s roles in thermal homeostasis is in evaporative cooling; i.e., releasing the body’s heat as sweat, which cools the body by using energy to transform the sweat from a liquid to a vapour, cooling the surface of the body thereby cooling the body down. Contrastingly, another homeostatic pressure exists in hot environmental conditions as a result of evaporative cooling: dehydration. Osmotic regulation becomes more difficult when the body is losing water rapidly to cool down. A solution would be to increase water intake, as a form of behavioural homeostasis, to allow osmotic homeostasis and thermal homeostasis to regulate themselves simultaneously. If there is no water being consumed to encourage hydration, then osmotic homeostasis is preferred and evaporative cooling reduces, meaning you sweat less, feel hotter, but don’t pass out from lack of water. In COLD environmental circumstances, there is less of a trade off between thermal and osmotic homeostasis, because cold weather does not have a pressure on hydration (osmotic homeostasis), since the skin is not likely producing sweat. The skin also has a role in cold weather thermal homeostasis by having hair as insulation.
Comparisons: the skin controls both osmotic and thermal homeostasis by releasing (or not releasing) heat energy as sweat onto the surface of the skin. The goal in both cases is to maintain your body’s homeostasis.
Contrasting: the goal of maintaining one homeostasis makes the other homeostasis harder to obtain, and the regulation of either requires the sacrificing of the other, to some extent and dependent on conditions. (= trade off)
Describe the five main anatomical components of the musculoskeletal system in terms of tissue type.
Bones, cartilage, ligaments, tendons, connective tissue
- Skeleton + muscles work together to support body weight & movement
- Skeletal: support, protect tissues, store minerals, generates blood cells
- Muscular: produce movement, support, generates heat
- Cartilage: supportive connective tissue w/ specialized support, found in surfaces between bones, ALSO in some non-bony cartilage (ears, nose)
- Ligaments: anchor BONES to bones
- Tendons: anchor MUSCLES to bones
- BOTH = bands of fibrous, dense, regular, connective tissue -
- Bone: supportive connective tissue
Compare and contrast the gross and fine anatomy of bone and cartilage with respect to structure and function.
Bone: the matrix in bone contains collagen (like cartilage) but also calcium salts, which makes it strong and relatively rigid. The matrix in bone is organized in concentric layers around blood vessels, in compact bone this is called osteons, in spongy bone it is called trabeculae. The medullary cavity (in the middle of the bone) contains bone marrow.
Bone cells:
- Osteogenic cells - undifferentiated bone cells - can become osteoblasts/osteocytes
- Osteoblasts - B for build, osteoblasts build new bone matrix
- Osteoclasts - C for chaos - osteoclasts destroy bone matrix - which releases calcium ions into the blood
- Osteocytes - bone cells within the matrix
Cartilage: cartilage is considered supporting connective tissue, provides flexible support for the body, and can be found between bones and also in some non-bony structures (like ears/nose). Cartilage is a solid rubbery matrix, and can be further subdivided into
- Hyaline cartilage - found between the tips of bones
- Elastic cartilage - support the ear + inner structures
- Fibrocartilage - dense and tough, found between vertebrae
- Chondrocytes (cartilage cells) are the only vascularized cells, and are found in the lacunae (holes in the matrix)
- Chondroitin sulfates combine with proteins to create proteoglycans, and form the matrix.
Bone and cartilage are grouped together because of the density/solidity of their extracellular matrix.
Compare and contrast the different mechanisms of growth that occur in bone and cartilage, including when they can and cannot occur.
Bone Growth: bone in fetal growth → the first bones are formed by the ossification of the cartilage, which starts when blood vessels invade the cartilage, starting with long bones. Then the ossification creates concentric rings of bone around those blood vessels. First the ends (epiphysis) ossify, but the metaphysis (or shaft) remains cartilaginous, and grows via interstitial growth until puberty, which continues to elongate the shaft. Bone CANNOT grow anymore after puberty because the epiphyseal plate ossifies during puberty and creates a physical barricade to further elongation. (sesamoid bones are formed through the ossification of non-cartilaginous joints - patella is an ossified tendon)
Cartilage Growth: cartilage is the first thing to appear in a growing fetus. Both appositional (by adding new layers of tissues to the outside) and interstitial growth (growing from within) occur before birth. Interstitial growth occurs when the chondrocytes undergo division, then secrete additional matrix which creates physical distance between the chondrocytes, and the new matrix is formed. In appositional growth, cells differentiate into chondroblasts, which secrete new matrix and then mature into chondrocytes, adding new cells to the exterior.
Explain the role of bone as a mineral reservoir and predict how bone cells will respond to changes in body calcium levels.
Bones are made of a collagen and calcium phosphate matrix which serve as a mineral reservoir, mainly for Calcium, that is regulated by hormones made by the parathyroid (PTH or parathyroid hormones) and the thyroid (calcitonin).
Calcium ions can be taken from the bloodstream and stored in the bones/ or removed from the bone matrix and put into the bloodstream in order to maintain homeostasis.
Balance between osteoblast and osteoclast activity maintains CA2+ homeostasis.
DECREASING BLOOD CA2+ LEVELS: parathyroid hormone is released and triggers increased osteoclast activity (it binds to osteoblasts and they release a hormone RANKL, that matures the osteoclasts so they can get to work). Increased osteoclast activity = more bone breakdown = more disposable Ca2+ ions to enter the bloodstream.
INCREASING CA2+ LEVELS: thyroid secretes calcitonin, which restricts osteoclast activity. Less osteoclast activity = less bone breakdown (balance between clasts and blasts is disrupted, so the osteoblasts are building more bone than osteoclasts are taking apart bone), so Ca2+ is turned into bone matrix, and removed from the bloodstream.
Compare and contrast the processes and potential for repair in bone and cartilage.
BONE REPAIR: highly vascular
- Blood clot is formed (fracture hematoma)
- Osteogenic cells proliferate, newborn cells colonize the damaged area
- First cartilage, then spongy bone appears
- The ends (or cartilage and bone) reunite (usually within 2-4 weeks)
- External colossus is visible, and it can take months-years for the spongy bone to reform into a compact bone.
CARTILAGE REPAIR: avascular , rarely repairs itself in adulthood, and if/when it does it is only via appositional growth.
Discuss the causes and treatments of osteoarthritis.
Osteoarthritis = caused by damage to articular cartilage (which we know can’t repair very well) a degenerative arthritis, the most common form, affecting mostly people 60+ as a result of cumulative wear and tear on joints or genetic factors affecting collagen formation.
Treatment:
a) regular exercise (more stress on the bones from the muscles pulling on them = more chances for the bones to rebuild)
b) physical therapy (like massage of electrical stimulation TENS)
c) anti-inflammatory drugs like aspirin
d) last case scenario is artificial joints, which can restore mobility and relieve pain. Can last more than 15 years, but high impact activity is prohibited (jogging, running, playing sports)
Explain the basic definition of muscle tissue and compare between its subtypes.
Muscle tissue is a tissue made from cells that are specialized to contract and produce movement/mechanical force.
Skeletal Muscle: striated, voluntary and moves the body by pulling on bones. Also maintains body temp, provides stability in posture and body position, stores nutrients, guards body entrances and exits (sphincters) and supports soft tissue.
Cardiac Muscle: striated, involuntary and found in the heart. Contractions allow blood to be pumped through blood vessels.
Smooth Muscle: non-striated, involuntary, found in the walls of hollow organs like the digestive tract where it moves food and fluid along
Describe the organization of skeletal muscle and the tissue types that is is made from.
From smallest to biggest:
- Myofibrils (protein filament) bundled together create a muscle fiber, this is what is actually doing the contraction
- Muscle fiber (myofiber) - contains multiple nuclei, surrounded by the endomysium
- Endomysium - areolar connective tissue that surrounds each muscle fiber, contains capillaries, myosatellite cells (stem cells that repair damage) and axon of the neuron that controls the muscle fibers.
- Many muscle fibers together = fascicle
- Perimysium - fibrous layer that divides the fascicles from each other. Contains collagen and elastic fibers and also blood vessels and nerves that supply the muscle fibers within the fascicles
- Many fascicles together = a muscle! Generally a fascicle is made up of 20-60 muscle fibers.
- Epimysium - a dense layer of collagen that surrounds muscles to separate them from organs and surrounding tissue. Connected to deep fascia (dense connective tissue layer)
- All muscles are surrounded by fascia.
Contrast the features of a myofibre that make it unusual to the properties of most cells in the body.
**Multiple nuclei** - because they are developed through the fusion of myoblasts, the end product contains multiple nuclei. As many as 3000 per fiber! Myoblasts that don’t fuse into multinucleated myofibers become myosatellite cells (stem cells that repair damage)
Significantly bigger than most other cells
Plasma membrane in myofibers is called “SARCOLEMMA” and cell contains SARCOPLASM instead of cytoplasm
Name the specialized parts of myofibers (including organelles and specializations of the cell membrane).
myofiber - a muscle cell
sarcomere- one full unit of a thin filament and a thick filament in a myofibre. (½ I-band + A band + ½ I-band)
sarcolemma- the plasma membrane, the site that is closest to the NMJ and receives ACh binding, triggering sodium movement / depolarization
sarcoplasmic reticulum - like the cytoplasm but muscle specific, stores a bunch of calcium which it releases via the sodium binding to DHA protein which then moves the RYA (?) protein when sodium floods down from the t-tubules
myofibril- the bundles of fibres that exist within a myofiber (20-100 per cell, i think) that are held by endomysium- a bundle as a unit is a fascicle.
thin filament
thick filament
motor end plate
neuromuscular junction
nerve fibres
blood vessels
myosatellite cells - stem cells that repair damaged muscle fibers (active in ‘bulking’)
mitochondria
Explain the role of neurotransmitters and membrane potential in muscle excitation and predict the effects of drugs that interfere with different stages.
Muscle excitation is reliant on a neuron releasing acetylcholine, a neurotransmitter, into the neuromuscular junction. The acetylcholine binds to nicotinamide channel proteins in the membrane of the skeletal muscle cell; these channels allow sodium to rush into the cell from the NMJ when a small increase in sodium ion membrane permeability leads to a set threshold of -55mV in neurons.
Analyze why artificial stimulation is used to build and maintain muscles.
The electrical stimulation works at the level of the integument, sending an electrical pulse which simulates a nerve impulse that leads to muscle excitation. The muscle excitation will not be large enough to actually move a large muscle group, but it can work effectively for small contractions which do not strain other parts of the structure (like tendons and ligaments) which is great for injured athletes or bedridden individuals who do not want to add additional strain / weight strain onto fragile parts of their bodies, but that do want to preserve or even build their muscles. The small contractions that are coming via electrical impulse to the neurons which then fire an impulse to stimulate contraction can cause tiny tears in the muscle which must be repaired by the formation of new muscle fibres; this causes each piece of the torn muscle to join, repairing the muscle and in that making the muscle larger.
Describe the arrangement of filaments in myofibril/sarcomere, and the key features of thin and thick filaments.
M line: Connects the central portion of each thick filament
H band: lighter region on either side of M line, consists of thick filaments
A band: The dark region of a sarcomere that contains thick filaments
I band: The light region of a sarcomere that contains thin filaments (doesn’t overlap w/ thick filaments)
Z line: boundary between adjacent sarcomeres, consist of actin in which interconnect thin filaments of adjacent sarcomeres
Thin filaments look like a double helix and consist primarily of actin. Calcium binds to troponin, which causes tropomyosin to move away from the actin active site and allows myosin to interact with actin → begins contraction cycle
Thick filaments are primarily composed of myosin and a titin core
Explain the steps of the contraction cycle, including the roles for calcium and ATP.
The transition from excitation to contraction begins when action potentials pass T-tubules, causing an electrical signal which triggers the release of calcium ions previously stored in the sarcoplasmic reticulum. The calcium then binds to troponin, causing tropomyosin to move away from the actin active site. Myosin is now able to bind to the actin active site, form a cross bridge, and complete a power stroke. The cross bridge cannot be broken until a new ATP molecule binds to the myosin neck.
Analyze how the sliding filament model of sarcomere predicts different amounts of muscle tension depending on muscle length.
Basically, if there’s no overlap between the filaments (if the muscle is already totally extended), the muscle will only be able to contract and shorten the muscle a little bit because the maximum capacity of contraction. And same goes is the muscle is already fully contracted, (short) there’s no wiggle room for it to get even shorter.
Explain what is occurring in each of the three phases of a muscle twitch, and why overlapping stimuli can summate to produce tetanic contraction.
Three phases of twitch stimuli: latent period, contraction, relaxation
LATENT PERIOD; the amount of time the motor neuron takes to release ACh into the NMJ, as well as the time it takes for sodium to flood the cell and move down the t-tubules / sarcoplasmic reticulum
CONTRACTION: steadily increases as more calcium floods in, exposing multiple binding sites for myosin heads to bind to, myosin binding to them, this process accounts for the steep but steady rise until peak contraction / force is reached.
RELAXATION: Ca2+ is steadily removed from the sarcomere, which returns all exposed binding sites to being covered by troponin and tropomyosin. ATP continues to reposition the myosin neck. ‘peak relaxation’ (resting period) occurs when all active sites are blocked once more.
Tetanic contraction occurs when ALL possible G-actin binding sites are exposed and bound to myosin heads; this is the highest point of contraction that cannot be superseded, the ceiling of contraction. If tetanic contraction is a plateau at the top of the graph, and an initial twitch is near the bottom, there is all of the space in between where a contraction can increase each twitch that occurs; this happens as more and more calcium is being released from the SR, exposing more binding sites and adding more “little men” to pull the rope.
Define the term ‘motor unit’ and discuss how multiple motor units are recruited during synchronous and asynchronous recruitment.
Motor units refer to the motor neuron plus ALL of the muscle fibres that the motor neuron contacts - one motor neuron can contact up to 100 muscle fibres, but one muscle fibre can only have one corresponding motor unit.
In synchronous recruitment, motor units are recruited by size; smaller units first, and then medium sized units, and then large units - large units take A LARGE stimulus in order to recruit and for the corresponding muscle fibres to contract.
In asynchronous recruitment (pattern of firing motor neurons to prevent fatigue) when a muscle must sustain a contraction for minutes or more, motor units take turns being active and contracting, and then relaxing until its their turn again - this conserves stores of ATP and calcium so that no one motor neuron (/muscle fibre) runs out of stores and is unable to keep contracting, allowing the contraction to continue for a longer period of time.
Describe how anatomical and physiological features can differ between different muscles and discuss how these affect tension generation.
Basically, three ‘size’ components matter where the largest has the most tension generation: motor neurons (more motor neurons active = more force and tension), more fascicles per myofiber, and more myofibrils per fascicle.
Because the myofibrils are the location of the thin and thick filaments which are the base unit of a muscle contraction; each of these categories will increase in myofibril amount if the overall unit gets bigger, meaning that the overall contraction will increase.
Hypertrophy → more myofibrils per myofiber , which is the only kind of growth that can occur in adults hyperplasia → more myofibers in general.
Also, there are different arrangements of muscle fibres in a muscle group: parallel arrangement, or pennate arrangement.
Parallel arrangement has shorter tendons that exist on each end, with all fascicles being parallel to the long end. Contrastingly, pennate muscles have longer tendons and fascicles are only parallel to the one end, so they can look different (unipennate, bipennate, or multipennate). This means that there are MORE muscle fibres pulling one tendon than in a parallel muscle; the pennate muscle will have shorter fibres but more force on that one tendon. More force in a pennate. Remember that the direction and amount of fibres on the individual tendon will both affect the overall tension.
Explain how muscle shortening can occur at different speeds or reverse depending on the load of the muscle.
A muscle always has to contract with enough force to change the weight of itself, PLUS the weight of the load; this means that it will take a longer time for the muscle to shorten the heavier the weight is. Also, I suppose that it does take some time for the excitation contraction cycle to occur, so perhaps adding a bunch of latent periods together might take a longer time. A flex of a large muscle will take a lot of energy and activate many motor units so I suppose that would take some time to rally. Also, muscle shortening does not always happen, if there’s a balance from gravity where the muscle simply does not want to extend but also not shorten, that is an isometric contraction. Eccentric contraction produces tension and gets longer but not as long as it would get if it wasn’t doing any contraction at all. A good example is ‘braking’ so that you can be cushioned against the force of gravity as you ascend.
Compare and contrast the different mechanisms skeletal muscles use to generate ATP when these mechanisms are used.
Muscles generate ATP aerobically or anaerobically by breaking down (catabolism) of glucose/glycogen, lipids or other organic molecules.
Aerobic Metabolism: occurs in the mitochondria and requires a supply of oxygen, but can generate lots of ATP (>30) from a single glucose molecule and can also metabolize fatty acids but requires more time.
Anaerobic Metabolism: can occur in the cytosol and does not require an oxygen supply, it can only use glucose and generates less ATP per molecule of glucose, but can work very quickly and without oxygen.
Phosphocreatine: can be used to very quickly convert ADP to ATP, but the stores of this molecule are really small and so it is used up very quickly.
*Trade off exists between how much ATP can be generated/with how quickly it can be obtained*
Resting Muscles use aerobic metabolism to build up a supply of ATP and also increase phosphocreatine levels and glycogen levels.
Moderately active muscles can have ATP needs met by the slower pace of aerobic metabolism.
At peak activity, muscles require additional support through glycolysis (anaerobic) or CP - both of which create waste products.
Define the term ‘muscle fatigue’ and identify at least two physiological changes that contribute to it.
Muscle fatigue is when you use your muscles close to peak activity over and over and over again and they stop performing at the same rate; this affects both excitation and contraction in ways that are detailed below.
Fatigue refers less to the below affects actually happening (specifically hydrogen running free in the cell), and more to homeostatic regulation that tells motor neurons not to contract, as that prevents actual damage to the bottom.
What DOESN’T contribute to muscle fatigue is running out of ATP; this only happens when you die. everything else happens first!
EXCITATION FATIGUE CONTRIBUTORS: - Potassium starts to build up outside of the cell here in the t-tubules where is is hard to diffuse away into the ECF; this affects the ability of the sarcoplasm to undergo more action potentials - Also, the depletion of ACh (neurotransmitter) from the motor neurons. You can run out of ACh temporarily and the motor neuron cannot perform its excitation stimulus because of this.
CONTRACTION FATIGUE CONTRIBUTORS: Lactate and hydrogen ions build up in the cytoplasm; can affect how calcium interacts with tropomyosin which affects the formation of cross-bridges. - leaking of Ca2+ into the sarcoplasm; pump does not allow Ca2+ to get back into the SR…. affects like not being able to relax.
Muscle Fatigue: a muscle is fatigued when it can no longer perform at the required level of activity. (when rapid ATP production affects the ability of the muscle to maintain the contraction cycle)
Identify the key anatomical and physiological features that distinguish between Type I and Type II muscle fibres and analyze how these would contribute to performance differences and training effects.
Type 1 (slow twitch) Not as powerful, but fatigue resistant
- more capillaries per muscle fibre = more oxygen supply
- More mitochondria = more ability to produce ATP
- Fewer Myofibrils = lower max tension
- Maximum twitch develops slowly but it maintained longer (calcium+myosin pump)
Type 2A (fast twitch) High force and rapid contraction, but fatigue easily
- Fewer capillaries = less oxygen supply
- More myofibrils = higher max tension
- Less mitochondria = less efficient ATP production
- Maximum twitch develops quickly, but is not maintained for long
Type 2B: intermediate twitch, somewhere in between type 1 and type 2a.
- Does not fatigue incredibly quickly, but also does not fire incredibly quickly.
Describe the three anatomical divisions of the nervous system in terms of location and connectivity.
CNS - Central Nervous System, located in the brain and spinal cord
- Processes information from the sensory neurons (found in PNS) integrates that info, then sends signals to the motor neurons (found in PNS) to respond PNS
Peripheral Nervous System, located in all other nervous tissue
- Detects stimuli from via sensory receptor neurons in peripheral tissue and translate the stimuli to action potentials that travel to the brain/spinal cord (CNS)
- Respond to commands from the CNS through motor neurons that carry information from the CNS to peripheral tissues (muscles, organs etc) ENS
Enteric Nervous System, located in the GI tract and mostly control digestion
- Only partially connected to the CNS, but is capable of operating without intervention from the CNS, however information from the CNS can alter normal digestive function
Explain the functions of the four compartments of a neuronal cell and classify a neuron based on the number and arrangement of its neurites.
Neurons = information transfer (vs glial cells which play support roles), also neurons are highly polarized
- Cell Body: receives info and produces proteins
- Dendrite: receive input/information from other cells
- Axon: transmits action potentials to surrounding cells (also has key components to information transfer the axon hillock, initial segment)
- Axon Terminal: convert electrical action potentials into chemical signals (neurotransmitters)
- Can be characterized based on the arrangement of it’s neurites into:
- Multipolar neurons: many dendrites and 1 axon (most common, most neurons are multipolar)
- Bipolar neurons: 1 dendrite and 1 axon
- Unipolar neurons: axon is only attached to the cell body in one spot (as opposed to the axon passing through the cell body giving it to different connection points with the soma)
- Anaxonic neurites: rare, but have dendrites and axons that combine functions - sending and receiving information
Explain the functions and key structure features of four different types of glia.
Glial cells = support roles + neuron maintenance (vs neurons that carry info); the following 4 are the glial of the CNS.
Ependymal Cells: mainly produce, monitor and circulate CSF (cerebrospinal fluid)
Microglia: mobile cells (like macrophages) that remove pathogens, waste and cellular debris through phagocytosis (engulfing it so it can be processed) and modify connections between neurons
Astrocytes/Satellite Cells: maintain the BBB, also structural support, regulate dissolved ion/gas/nutrient content in interstitial fluid around neurons, and absorb and recycle neurotransmitters that aren’t reabsorbed/broken down at synapses
Myelinating cells (Oligodendrocytes and Schwann cells): structural framework and also produce myelin sheath.
Compare and contrast the capacity of neurons in the CNS and PNS for repair.
In both situations, if the cell body of a neuron dies, the whole neuron will die. But if an axon is damaged it has the capacity to regrow, IF it is an axon in the PNS.
PNS: contains different glial cells (Schwann Cells and Satellite cells) Because of the Schwann cells, PNS neurons are more easily repaired because the Schwann cells do not degenerate and instead they proliferate along where the axon used to be. Macrophages remove debris, and then the axon begins to regenerate and follows the ‘tunnel’ that has been created by the Schwann cells. If the axon reestablishes connection, then function can return to normal.
CNS: nerve repair is much more limited because a) more axons are likely involved in the damage than in the PNS, b) astrocytes produce scar tissue that can prevent the axon from regrowing and connecting with itself c) (is it oligodendrocytes or astrocytes?) release chemicals that block axon growth
Explain how a neuron’s transmembrane potential arises from differences in ion concentrations and permeability, including the roles of ion channels and active transport proteins (e.g., pumps).
Transmembrane potential is caused by the separation of positive and negative charges by the plasma membrane. If all ions were equally permeable there would be no transmembrane potential, because the ions would naturally flow to equalize themselves within the solution.
Generally the inside of a cell at rest is at -70 (70millivots less positive than the outside)
Outside the cell (ECF) lots of Na+ and Cl- ions (net positive charge)
Inside the cell (ICF): lots of K+ and Protein- ions (net negative charge)
Permeability: ions move through ion channels (because of their charge they are hydrophobic and can’t diffuse through the hydrophilic plasma membrane) so they move through ion channels/carrier proteins. Some of these channels are always open while others require a signal (whether it be ligand, mechanical, or electrically (voltage) stimulated) to tell them to open or close.
Role of Ion Channels: allow for ions to pass through the plasma membrane and enter the cell, which can create a change in the membrane potential, a graded potential.
Role of Pump/active transport pumps: stabilizes the neuron by bringing it back to its resting membrane potential, by sending 3Na+ ion out of the cell and bringing 2K+ back into the cell. This is important because the neuron is only ready to fire an action potential when ion distribution and membrane potential are at specific levels (most of the brains energy use is because of the pumps stabilizing neural membrane potentials).
Describe the key features of metabotropic receptor signalling and explain why the same receptor diversity means that the same neurotransmitter can have opposite effects on different effector cells.
- linked to intracellular proteins called G proteins, which initiate biochemical cascades to produce longer lasting responses, diverse biochemical effects in addition to membrane potential changes, and stimulatory or inhibitory responses.
Explain (using specific examples) the difference between hormonal actions that directly affect metabolic rate, and the hormonal effects that affect metabolism by mobilizing the nutrient pool.
- Thyroid hormone receptors can directly regulate BMR by affecting mitochondrial function.
- Some thyroid hormone receptors are found in the mitochondria, especially in skeletal muscle cells → when activated, these receptors upregulate mitochondrial activity, directly increasing ATP and heat production.
- Several other hormones indirectly affect metabolism by mobilization of nutrients from different cellular stores
- Epinephrine and glucagon → mobilize glucose and fatty acids from liver and adipose tissue
- Glucocorticoids and growth hormone → mobilize fatty acids from adipose tissue and promote lipid uptake as well as gluconeogenesis → glucose-sparing effect - promot use of lipids for metabolism by most cells so that available glucose is saved for the CNS
Analyze the effects of multiple hormones on the same regulated variable and classify them by the type of interactions.
- When different hormones produce changes in the same direction on a target variable, their effects can be purely additive, or synergistic (greater than the sum of the individual hormone effects).
- Glucagon + epinephrine = additive; Glucagon + epinephrine + cortisol = synergistic
Explain the roles of glucagon and insulin in maintaining normal blood glucose levels and how insulin secretion is regulated by blood glucose at a cellular level.
Glucagon → released by pancreatic alpha cells → stimulates gluconeogenesis and glyconenolysis in liver and release of glucose to plasma → increases blood glucose levels
Insulin → released by pancreatic beta cells → stimulates glucose uptake by cells and glycogenesis in liver → decreases blood glucose levels
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Beta cells act as sensors for blood glucose level. When blood glucose levels increase, the beta cells secrete insulin.
- Insulin decreases blood glucose level and acts as a negative feedback loop to decrease secretion of insulin by the pancreatic beta cells.
- Passive transport of glucose into beta cells is enhanced when blood glucose levels are high → leads to increased ATP production, which depolarizes cells.
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Beta cells at rest → The KATP channel (= a passive transporter that only moves glucose according to the concentration gradient) is open, and the cell is at resting membrane potential.
- When the potassium channel is open the voltage-gated calcium channels are closed and insulin remains in secretory vesicles inside the cytoplasm.
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Beta cell secretes insulin → closure of KATP channels depolarizes the cell, triggering exocytosis of insulin.
- When ATP levels are high, it binds the potassium channels and closes them so that the cell depolarizes and voltage-gated calcium channels open, resulting in secretion of insulin by exocytosis.
Explain the difference between stress and the stress response and describe how the nervous and endocrine systems are involved in triggering the stress response.
Stress → a situation that is perceived as a threat to homeostasis which produces the stress response
Stress response → an allostatic response to try and preserve homeostasis before it’s disrupted.
- The hypothalamus produces sympathetic activation of the entire sympathetic nervous system, which includes epinephrine (adrenaline) release from the adrenal medulla, and activation of the HPA axis which leads to the secretion of ACTH from the pituitary which leads to secretion of cortisol and other glucocorticoids from glands in the adrenal cortex.
- The amygdala is the ‘final decider’ about whether a situation is stressful or not, and whether a stress response occurs → once activated, the forebrain activates certain parts of the hypothalamus.
- Two major hormonal pathways activated by the stress response:
- Epinephrine → secreted by the adrenal medulla as part of sympathetic activation
- Non-hormonal parts of the SNS are also activated
- Cortisol → secreted from the adrenal cortex in response to HPA activation.
- Epinephrine → secreted by the adrenal medulla as part of sympathetic activation
Explain what is meant by ‘chronic stress’ and discuss how hypercortisolaemia can disrupt the HPA axis, and the process of sympathetic activation.
- Chronic stress is distinct from the exhaustion phase of a severe stress response → it is not immediately life threatening, but does lead to alterations in the stress response → the same kind of stressor will produce a higher sympathetic stress response in a chronically stressed individual than a naively stressed one, and the parasympathetic nervous system will not rebound
- Effects of chronic stress include:
- Weight gain
- Depression
- Memory loss
- Lack of concentration
- Sleep disturbances
- Susceptibility to infections
- Irritable bowel syndrome
- Thyroid imbalances
- Infertility
- Osteoporosis
- Chronic stress affects neural tissues → especially the hippocampus
- Prolonged exposure to glucocorticoids leads to a reduction in synapse numbers on hippocampal neurons → leads to disruption of HPA axis
- The hippocampus has an important inhibitory effect on CRH-secreting neurons in the hypothalamus
- The amygdala enhances CRH release
- If the hippocampus is damaged/less active, there will be less inhibition on CRH-secreting neurons to balance excitatory signalling from the amygdala, which leads to more cortisol release (positive feedback)
Compare and contrast X and Y chromosomes.
X-chromosome → protein coding genes: 1000-2000; one of the two X chromosomes is permanently inactivated during development (= X chromosome inactivation), so the genetic material becomes tightly compacted and inaccessible to transcriptional or translational proteins (= Barr body: dense heterochromatic structure formed by XCI in XX females)
Y-chromosome → protein coding genes: ~45; one of these genes is SRY, responsible for initiation male sex development
While X and Y chromosomes are vastly different in size and genetic material, two regions of homology, known as pseudoautosomal regions 1 and 2 exist and behave autosomally.
Know how SRY gene expression influences hormone production and sex determination in the growing fetus.
- The SOX9 gene (i.e., testes determining factor) is triggered to be expressed if (and only if) SRY has been expressed at the right time and in the right amount.
- In response to SOX9 expression in XY individuals, the primordial germ cells differentiate into sperm, and the supporting cells become Sertoli cells.
- Sertoli cells secrete Anti-Müllerian hormone (AMH), which is responsible for degrading the Müllerian ducts.
- On the other hand, primordial germ cells of the ovaries will develop into oocytes, and the supporting cell precursors develop into granulosa cells which do not secrete AMH. In the absence of AMH the Müllerian ducts do not degrade, but the Wolffian ducts do.
Describe how testosterone and estrogen are produced, and the role they play in sex development.
- In response to testes development in XY individuals, the steroidogenic cell precursors develop into Leydig cells and produce androgens (i.e., testosterone).
- Presence of androgens secreted within the developmental window in-utero causes the embryo to develop male external genitalia
- The steroidogenic cell precursors develop into Follicular cells in the ovaries and produce estrogens.
- The presence of estrogens secreted by the ovaries within the developmental window in-utero causes the embryo to develop female external genitalia
Compare and contrast male and female postnatal sex development before and after the onset of puberty.
- Secondary sex development is initiated by increased production of gonadotropin releasing hormone within the hypothalamus.
- GnRH then stimulates increased production of follicle stimulating hormone (FSH) and luteinizing hormone (LH)
- Prior to puberty, these hormones act on the gonads and exhibit a negative feedback loop which inhibits their production.
- At puberty, the negative feedback is removed and allows androgen production in the testes and estrogen production in the ovaries.
- Responses to Testosterone in males:
- facial hair
- accelerated bone deposition and skeletal growth → closure of epiphyseal cartilage
- increased muscle mass
- sex drive initated
- increased blood volume
- growth of larynx and lengthening/thickening of vocal cords → deep voice
- promotion of spermatogenesis
- Response to estrogen in females
- body hair in genital area
- more rapid epiphyseal closure than in males (females are not as tall)
- stimulated muscle growth (not to the same extent as in males)
- female sex drive initiated
- decreased plasma cholesterol levels
- higher pitched voice due to no excessive growth of larynx and vocal cords
- menstrual cycle onset
Explain the steps of spermatogenesis including the support cells, and the time course and location when/where different stages occur.
- As the developing gametes progress from spermatogonium to spermatocyte, spermatid, and finally sperm, they move from the basal layer of the seminiferous tubule (within the testes) toward the lumen, while maintaining contact with the Sertoli cells which provide the developing sperm with chemical signals and nutrients.
- Mitosis takes 16 days; Meiosis I completes within 24 days; Meiosis 2 occurs within hours; Spermiogenesis takes 24 days.
Explain the organization and regulation of the HPG axis for a typical female reproductive system, including changes in the pulsatile secretion over the ovarian cycle, sites of action for different hormones, and sources of negative feedback.
- LH is only secreted by gonadotropes when GnRH pulses are frequent and estrogen levels are high
- Stimulates thecal cells to secrete androgens
- FSH only requires GnRH stimulation for production and secretion
- Stimulates granulosa cells to secrete aromatase, which converts the secreted androgens to estrogens; granulosa cells also secrete inhibin which provides direct negative feedback on the secretion of FSH from the pituitary
- When estrogen levels are low → negative feedback on LH secretion
- When estrogen levels rise (driven by FSH), they act synergistically with GnRH to enhance LH secretion → positive feedback
- Progesterone (secreted by corpus luteum) has a primary role in negative feedback of GnRH secretion → when progesterone levels are high, GnRH release is very low
Name at least three hormones secreted by placental tissues, describe when their secretion is elevated, and explain their functions during pregnancy.
- Human chorionic gonadotropin (hCG) is secreted by the placental trophoblast very early in pregnancy; levels are highest during the first trimester; signals to the corpus luteum to survive; also promotes maternal immune tolerance of foetus
- After the luteal-placental shift (i.e., the corpus luteum becomes the corpus albicans and stops all hormonal secretions); the placenta begins progesterone secretions, which maintains the endometrium; decreases uterine contractions allowing for better implantation and growth; maintains endometrium, inhibits labour, and active lactation
- The placental trophopblast begins to synthesize estrogens as pregnancy progresses; plays a role in child birth and determining when the time is right by increasing prostaglandin production, and increasing myometrial activity to determine time of labour; increases blood flow to the baby; regulates receptors for other hormones
- Relaxin → alters blood flow and promotes ligament loosening (i.e., loosening of the pubic symphysis to allow a larger gap between hip bones for pregnancy)
Explain the neurohormonal basis of lactation, including the distinct roles of anterior and posterior pituitary hormones.
- Contraction of myoepithelial tissue around milk ducts is part of a neurohormonal reflex that leads to milk ejection and stimulates further milk production
- Hypothalamus secretes PIH → leads to release of prolactin from the anterior pituitary → milk secretion
- Hypothalamus also stimulates release of oxytocin from the posterior pituitary → smooth muscle contraction → milk ejection
- Mechanoreceptors in nipple, or the sound of a child’s cry, stimulate higher brain centers which trigger hypothalamus to secrete PIH and stimulate the posterior pituitary
