P.H.Y.S.I.O.

What is the stress response? This is the body's response to any external or internal threat (i.e. stress) that it receives. It involves three phases:    1.   Alarm Phase The alarm phase involves the high activity of the sympathetic nervous system (fight or flight). It is when norepinephrine and epinephrine are released, as well as glucocorticoids from the zona fasiculata. It results in: Decreased digestion Decreased urine production Increased heart rate Increased sweating Increased respiratory rate Changes in blood circulation Mobilisation of glucose stores    2.   Resistance Phase The resistance phase is when the stress remains for more than a few hours. It involves the use of alternative energy stores for organs, reserving glucose for the nervous system. The release of glucocorticoids and thyroid hormone dominates in the resistance phase, but NE and E are still released from the adrenal medulla. Glucagon is released also from t...

Regions of the brain Cerebrum - temporal, parietal, occipital, frontal lobes Cerebellum - cauliflower responsible for proprioception Diencephalon - hypothalamus (homeostatic control and neuroendocrine coupling) and thalamus (direction of sensory information to cerebral cortex) Brainstem - mescenphalon (hearing and sight), pons (inspiration), medulla oblongata (cardiovascular and respiratory centre) Receptors for general senses Nociceptors : pain and itch Thermoreceptors : temperature Chemoreceptors: chemicals, e.g. CO2 concentration Mechanoreceptors : tactile, baroreceptors and proprioceptors Ways of adaptation to a stimulus Tonic receptors : adapt slowly, always active Phasic receptors : rapidly adapting, switch off after a while Somatosensory pathway Somatosensory pathways are for the direction of information from general senses to the somatosensory cortex in the cerebrum. There are three pathways: Spinothalamic pathway (anterior and lateral) deliver...

Gigantism Overproduction of growth hormone in infants - adolescents Acromegaly Gigantism in adults (enlargement of mandible, growth of hands and feet) Goiter Enlargement of the thyroid gland Cretinism Congenital hypothyroidism (underproduction of thyroid hormone) which occurs in infants (protruding tongue, delayed puberty) Aldosteronism Overproduction of aldosterone (from zona glomerulosa) Myxoedema Hypothyroidism in adults (decreased mental ability, sparse, dry hair, puffy body areas) Grave's disease Hyperthyroidism (protrusion of eyeballs, heat intolerance, fatigue and weakness) Hypocalcaemia Too little parathyroid hormone (excitability of muscle tone, e.g. Chvostek's and Trousseau's sign) Hypercalcaemia Too much parathyroid hormone (depression of neuromuscular activity, softening of bones) Rickets Vitamin D3 deficiency with reduced bone density Cushing's Syndrome Increased ACTH or glucocorticoids...

Epidermal and Dermal Wound Healing Epidermal Wounding Healing: Basal cells of epidermis break contact with the basement membrane Cells enlarge and migrate across the wound, which is stimulated by epidermal growth factor (EGF) Migration of cells stops due to contact inhibition Relocated cells divide to build new epidermal layers and thicken epidermis Deep Wound Healing (into dermis and/or subcutaneous layer): Inflammatory phase : blood clot forms loosely binding wound edges, causing inflammation Migratory phase: clot becomes a scab, epithelial cells migrate beneath the scab to bridge the wound, fibroblasts migrate and form collagen Proliferative phase: extensive growth of epithelial cells beneath the scab, collagen fibres randomly deposited, blood vessels grow Maturation phase: collagen fibres become organised, epithelium is restored to normal thickness, scab sloughs off Photo damage There are three types of photo light, some which are blocked and some which ...

What is the dermis? The dermis is a connective tissue layer divided into two layers; papillary and reticular. The papillary layer is the more superficial layer composed of areolar tissue . It contains small capillaries, lymphatics and sensory neurons, as well as tactile corpuscles to detect light touch. The reticular layer is composed of dense irregular connective tissue (collagen, elastic fibres, connective tissue proper). It contains larger blood vessels, lymph vessels and sensory neurons and receptors called lamellated corpuscles (pressure and vibration receptors). The reticular layer shows us 'skin turgor', which determines hydration. NOTE: the hypodermis connects the dermis to underlying tissue. It is loose connective tissue with fat cells and large blood vessels. There is an absence of any vital organs or structures. Hair Hair, also termed pili, is composed of columns of dead keratinocytes held together by extracellular proteins. Parts of hair include: ...

What is the integumentary system? Basically, the skin! The integumentary system comprises a cutaneous membrane (skin), as well as accessory structures including hair, nails and exocrine glands. The skin has several functions: Protects underlying tissues and organs Excretes salts, water and organic wastes Maintains body temperature (insulation and evaporation) Synthesises vitamin D3 Detects touch, pressure, pain and temperature The skin is made up of three general layers: The epidermis : outer, thinner layer composed of epithelium (4-5 layers) The dermis : inner, thicker layer composed of connective tissue (2 layers) The hypodermis ( subcutaneous) layer: fat store with blood vessels and Pacinian corpuscles Below is a summary of the layers of the epidermis : Stratum corneum : dead keratinocytes arranged in multiple layers which are continually shed and replaced from deeper strata cells, water resistant Stratum lucidum:  exists in thick skin on...

So what do B cells do? B cells are responsible for antibody-mediated immunity, where pathogens are outside of the cell. B cells differentiate into plasma cells, producing specific antibodies to attack pathogens. There are millions of B cell populations, each with different antibody molecules. Antibody-mediated immunity is also called humoral immunity and is present from birth. Antibody-mediated immunity involves 3 steps:   1.   Sensitisation Sensitisation is when antigens bind to antibodies on an inactive B cell, making it sensitised. Recall that B cell membranes also contain Class 2 MHC proteins, which help in sensitisation by presenting the foreign antigen on the plasma membrane. The B cells is then on 'standby' until a helper T cell activates it.   2.   Activation Helper T cell binds to the class 2 MHC protein on the B cell, recognising the antigen and releasing cytokines to stimulate replication of the B cell and enhance antibody production...

What is adaptive immunity then? Adaptive or specific immunity responds to specific antigens through the coordinated action of T and B cells. It is only developed after birth. Adaptive immunity involves both cell-mediated and antibody-mediated immunity. Cytotoxic T cells provide cell-mediated immunity, providing defence against abnormal cells and pathogens inside  cells. B cells provide antibody-mediated immunity, providing defence against antigens and pathogens in body fluids. There are four properties of immunity: Specificity - response to only a specific type of antigen Versatility - production of many types of lymphocytes Memory - active lymphocytes stay in circulation and provide immunity against new exposure Tolerance - immune system ignores normal antigens What is cell-mediated immunity? T cells only recognise antigens that are bound to glycoproteins in a plasma membrane. These are termed major histocompatibility complex proteins. These proteins differ betwee...

What is innate or non-specific immunity? Innate immunity got its name because of the fact that it always works in the same way and is against any type of invading agent. It is a non-specific defence. There are seven major categories of non-specific defence:   1.   Physical Barriers These include skin, hair, epithelial layers of internal passageways, secretions to flush away materials and secretions to kill or inhibit pathogens.   2.   Phagocytes There are two types of phagocytes; microphages, which are small and leave the bloodstream to fight infection, e.g. neutrophils, and macrophages, which are large cells distributed through the body. Macrophages are produced from monocytes and once activated, respond to pathogens in several ways:   a.   Engulf pathogens and destroy using lysosomal enzymes   b.   Bind to pathogens so other cells can destroy it   c.   Destroy pathogens by releasing toxic chemicals into the i...

Introduction Pathogens are microscopic organisms that cause disease, e.g. viruses, bacteria, fungi and parasites. Antigens are targets that identify any pathogen or foreign compound. The lymphatic system  protects us against disease. Lymphocytes, the cells of the lymphatic system, respond to environmental pathogens, toxins and abnormal body cells, e.g. cancerous cells. The immune system  involves immunity, the ability to resist infection and disease. All body cells and tissues are involved in the production of immunity. The primary function of the lymphatic system is to produce immunity, and maintain and distribute lymphocytes. It is also a drainage network which maintains fluid balance between tissues, and absorbs fats from the digestive system. Components of the lymphatic system are described below: Lymph : fluid similar to plasma Lymphatic vessel : carry lymph from peripheral tissues back to the venous system Lymphoid tissues and organs: ...

What happens when we give birth? During the last week of pregnancy, oestrogen reaches a peak. This causes myometrial weakness and irritability. Then, weak 'Braxton Hicks' contractions occur, which become uterine contractions stimulated by oxytocin and prostaglandins closer to birth. Emotional and physical stress establishes a positive feedback mechanism with the hypothalamus, increasing oxytocin release. The stages of labour are summarised below:   1.   Dilation Stage (8 hours) Onset of labour Cervix dilates Foetus moves towards birth canal Contractions begin and increase in frequency Water eventually breaks   2.    Expulsion Stage (2-3 hours) Cervix pushed open by foetus Contractions increase in intensity, frequency and length Continues until foetus emerges from vagina (delivery) Surgical intervention possible: episiotomy (cutting of perineal membrane) or caesarean section Newborn health assessed immediately   3.   Plac...

How does the female body respond to pregnancy? The maternal body must adapt to provide the environment, nutrients, waste removal, buoyancy and respiratory gasses for the developing embryo/foetus. Maternal changes to physiology include:   1.   Metabolic Changes hPL stimulates breast maturation and mammary gland preparation hPL results in glucose-sparing effect, which affects lipid and carbohydrate metabolism, meaning glucose is reserved for the foetus Increased appetite (10-30%)   2.   Cardiovascular Changes Blood volume increases 25-40% Increased cardiac output Decreased total peripheral resistance Decreased blood pressure   3.   Renal Changes Enlarged kidneys Dilated ureters Increased urine production 50% increase in glomerular filtration rate Unregulated renin-angiotensin system → increases aldosterone levels → water and sodium retention   4.   Respiratory Changes Increased respiratory rate and tidal ...

How does the placenta form? The placenta forms from the embryonic trophoblastic/mesoderm tissues, as well as the maternal endometrial tissues. Vessels develop in the embryonic tissues which then supply nutrients to the foetus from the maternal blood supply. The chorion develops fingerlike villi which have become vascularised and extend to the embryo as umbilical arteries and veins. The embryo, amnion and yolk sac float in a fluid-filled chamber attached to the placenta by a body stalk. The placenta grows and begins to develop into organised regions, bulging into the uterine cavity as it grows. It becomes fully developed by the end of the third month (end of first trimester), where the foetus moves farther from the placenta connected by the umbilical cord. By 12 weeks, the placenta is providing nutrients and removing wastes, meaning it takes on the role of oestrogen and progesterone which used to be released from the corpus luteum. Decidua capsularis: endometrium surroundi...

Terms Pregnancy : events that occur from fertilisation until the infant is born Conceptus : the developing offspring, i.e. bound end and sperm regardless of the stage of pregnancy Gestation period : from the last menstrual period until birth Pre embryo:  conceptus from fertilisation until 2 weeks of age in mother Embryo:  conceptus during weeks 3-8 Foetus : conceptus from 9 weeks until birth What happens during fertilisation? The oocyte is only viable for 12-48 hours. The sperm are viable for no longer than 24-72 hours. For fertilisation to occur, coitus (conception) must occur no more than 3 days before ovulation and 24 after ovulation. Fertilisation occurs when a spermatozoon fuses with a secondary oocyte to form a zygote. Two haploid gametes therefore are forming a zygote. An ovulated oocyte, as mentioned in Female Reproductive System posts, is encapsulated by the corona radiata and zona pellucida, as well as the extracellular matrix. A sperm ...

Structure of a sperm  What is the function of nurse cells (sertoli cells)? Nurse cells, also termed sustentacular or sertoli cells, play a key role in spermatogenesis through: Maintain of the blood-testis barrier (through tight junctions with outer basal layer and inner luminal compartment) Support mitosis and meiosis (through FSH and testosterone) Support spermatogenesis (surround spermatids, providing nutrients and stimulating development, phagocytose and shed cytoplasm of spermatids) Secrete inhibin (to depress FSH secretion) Secrete Androgen-Binding Protein (binds to testosterone, elevating concentration of hormones in the seminiferous tubules) Secrete Müllerian-Inhibiting Factor (descent of testes during birth) Leydig cells (interstitial cells) are in between the seminiferous tubules and secrete androgens, most importantly in males, testosterone. Testosterone and hormonal control Testosterone is synthesised from cholesterol in Leydig cells and is release...

What is the point? The male reproductive system, although significantly less complex than the female equivalent, has two critical functions: To produce haploid spermatozoa To deliver spermatozoa into the uterus and fallopian tubes, enabling fertilisation and production of an embryo Components of the system Below is a summary of each structure in the male reproductive system: Testes:  have an endocrine function and produce spermatozoa Epididymus : spermatozoa are matured (18 hours to 10 days) and stored in the epididymus Ductus (vas) deferens : spermatozoa are stored and passed through here from the testes to the ejaculatory duct Urethra : passageway for urine from the bladder, receive spermatozoa/semen from the ejaculatory duct Seminal glands (vesicles):  secrete most of the fluid that makes up semen, drains into the ductus deferens Prostate gland : produces prostatic fluids which mix with seminal fluids in the urethra Bulbourethral gla...

What are the stages of the menstrual cycle? Proliferative Phase : Oestrogen is produced by the follicle, promoting proliferation of the endometrium epithelial cells. Replacement of the functional zone of the uterus begins. Secretory Phase : After ovulation, the corpus luteum secretes progesterone. The uterine glands increase their secretion and the endometrial lining is thickened. The secretory phase lasts 14 days. Menses: Menses occurs when it is a non-pregnancy case. There is a hormone level drop where the functional zone of the uterus is shed (stratum functionalis is sloughed off). The layer is shed because the endometrial blood vessels become constricted and there is decreased oxygen and nutrients supplied to the lining. The cells disintegrate and blood escapes from the damage capillaries, and with the cellular debris this makes up the menstrual fluid. A new ovarian cycle begins during menses. Combined Oral Contraceptive Pill The combined oral contracept...

Hormones Oestrogens are responsible for female secondary sexual characteristics and bone and muscle growth. Oestrogens influence the production of cervical mucus and the structure of the vaginal epithelium. This encourages growth of bacteria, which are responsible for the acidity of the vaginal fluid. Estrogens cause the proliferation of the uterine endometrium, encourage fluid retention and inhibit FSH. Estradiol  is the main oestrogen, although others include estrange and estriol. Progesterone  only acts on tissues which have been previously acted on by oestrogen. Progesterone causes endometrial growth, secretory changes in the lining of the uterus and causes the body temperature to rise half a degree after ovulation. Follicle stimulating hormone  increases follicle development and stimulates inhibit and oestrogen secretion. Before day 10 of the ovarian cycle, the secretion of oestrogen inhibits the secretion of LH. However, after day 10, oestrogen stimulate...

What is the point? The female reproductive system has several important functions, all of which are summarised below: To provide haploid ova (oocytes) To provide an environment for the fertilisation and development of ova To expel offspring from the body To provide the initial nutrition to the offspring my lactation. The parts of the female reproductive system are all simplified below: Ovaries : have an endocrine function, produce oocyte Fallopian tubes : transport and nourish oocyte, most common site of fertilisation with spermatozoa Uterus:  mechanical protection, nutritional support and waste removal for embryo/foetus, contraction during childbirth to eject the foetus Vagina:  muscular tube that allows for the elimination of menstrual fluids, holds spermatozoa after sexual intercourse, final portion of the birth canal. Vulva:  includes the vestibule, labia major, labia minor and mons pubis, vaginal opening, urethral opening and the clit...

Hormones Antidiuretic hormone  (vasopressin) controls fluid concentration and is important in preventing changes in cell volume. ADH reacts rapidly to changes in the extracellular fluid concentrations and regulates water reabsorption in the collecting duct (meaning it also causes sodium reabsorption). ADH is released in response to increased plasma/ECF concentration. It stimulates the incorporation of aquaporins in the distal convoluted tubule and collecting ducts, and allows for water to be reabsorbed. ADH is produced in the hypothalamus and is released from the posterior pituitary gland. Aldosterone  controls sodium reabsorption, and because water moves with sodium, aldosterone therefore controls fluid volume. This is important in regulation of blood pressure. It is slower acting than antidiuretic hormone. Aldosterone acts by incorporating Na+ and K+ pumps in the distal convoluted tubule and cortical region of the collecting duct. pH The extracellular fluid pH i...

Fluid Homeostasis On average, the extracellular fluid, i.e. the peritubular fluid, has an osmolarity of 300mosm/L. This means it has a certain number of solute molecules per litre of water in the fluid. Below is a summary of how and where solutes and water are reabsorbed along the nephron system. Proximal Convoluted Tubule 65% Na+ and 65% H2O Sodium reabsorption provided by: Epithelial Na channel (ENaC) Co-transport with glucose (SGLT) Exchange pump for Na+ and K+ Water reabsorption provided by: Osmosis Nephron Loop (Loop of Henle) 25% Na+ and 15% H2O Sodium reabsorption provided by: Co-transport with K+ and Cl- ions ( thick ascending limb only ) Exchange pump for Na+ and K+ Water reabsorption provided by: Osmosis ( thin descending limb ) NOTE: The thick ascending limb has a high efficiency when pumping Na+ out of the tubular fluid alongside potassium and chloride ions. It is impermeable to water and decreases the tubular fluid concentr...

Autoregulation (at the local level) Autoregulation maintains the glomerular filtration rate despite changes in local blood pressure and blood flow. It does this by altering the diameters (lumen width) of the afferent and efferent arterioles, as well as the glomerular capillaries. The arterioles are changed through a myogenic mechanism, whereas tubuloglomerular feedback is responsible for changes in the glomerulus. The myogenic mechanism involves stretch receptors: ↑ blood pressure → afferent arteriole wall stretches, smooth muscle contrasts, afferent arterioles constrict, ↓ glomerular blood flow and pressure → ↓ net filtration pressure → ↓ glomerular filtration rate (see 1) ↓ blood pressure → dilation of afferent arteriole and glomerular capillaries, constriction of efferent arteriole, ↑ glomerular blood pressure → ↑ net filtration pressure → ↑ glomerular filtration rate (see 2) The tubuloglomerular feedback mechanism ...

What forces govern glomerular filtration? Glomerular filtration involves passage across a filtration membrane. This filtration occurs through capillary endothelial pores, which are leaky but not overly selective. The solutes then enter a dense layer or Basal Lamina, which is a collagen matrix that separates the cells of the capillaries from those of the Bowman's capsule (tubule). The basal lamina prevents large proteins from crossing, but allows water and solutes to move across. There is also reasonable dependence on charge when it comes to determining what is able to move through this layer. The solutes must then pass through filtration slits created by spaces between podocytes, which line the Bowman's capsule. Hence, Water and solutes build up in glomerular capillaries Substances move through pores in capillary endothelium into basal lamina Filtration slits between podocytes map route for substances into Bowman's capsule In order for glomerular filtration ...

What is the Renal System? The renal/urinary system is made up of the kidneys, ureters, bladder and urethra. The five basic functions of the renal system are: Water and ion balance Excretion of metabolites and foreign chemicals Regulation of blood pressure Sodium balance Renin-angiotensin system Regulation of red blood cell production (erythropoietin) Regulation of vitamin D activity However, the two basic functions of the kidney are: Concentrate the filtrate in the nephrons by altering tubular secretion and tubular reabsorption of water and ions Absorb and retain valuable materials for use by other tissues (sugar and amino acids) The nephron is the functional unit of the kidney, and there are two types of nephron with the same function; cortical and juxtamedullary nephrons. Both these nephrons function to maintain a water and ion balance. The tubule of a nephron runs across the axis of the cortex to the medulla, and is surrounded by a capillary network...

By the cell and hormones The generation of energy produces 60% heat and 40% ATP energy. Cells regulate the entry of substances depending on their needs. The rate-limiting step in energy production is where fructose-1,6-biphosphate is produced. This molecule is involved in the regulation of metabolism, in association with an enzyme called phosphofructokinase . Phosphofructokinase is an enzyme that adds a phosphate group onto fructose-6-phosphate molecule. This makes it the previously mentioned fructose-1,6-biposphate. It has multiple binding sites on it, specifically for ATP, ADP and citrate. The binding of ADP moves the reaction forward, although binding of ATP inhibits the process, restricting glycolysis. Citrate, a product of the Krebs cycle, also inhibits the production of fructose-1,6-biphosphate. This means that there is nearly a negative feedback mechanism to restrict the process of glycolysis. Pyruvate dehydrogenase is another enzyme that controls the rate of progression ...

What happens without oxygen? Without oxygen, cells require alternate electron acceptors to allow oxidation of NADH and FADH2. Unfortunately, this means less energy is generated than aerobic respiration and oxygen is no longer the terminal electron acceptor. Alternate electron acceptors include carbon dioxide, sulfates and the fermentation of organic molecules in eukaryotes. Anaerobic respiration and fermentation are two terms used interchangeably, the first referring to lactic acid production and the latter referring to alcohol fermentation using yeasts. The process of energy production in anaerobic respiration is not completely different to aerobic respiration in that glycolysis still occurs, where one glucose molecule is catabolised to produce 2 pyruvate molecules. Recall that pyruvate is required, as it can enter the mitochondria. However, instead of entering the citric acid cycle, pyruvate enters fermentation which produces either ethanol (alcohol) or lactic acid. This fermen...