Homeostasis, pregnancy and fertility Flashcards
Homeostasis
Maintenance of a constant internal environment
Conditions of internal environment controlled in mammals
- Body Temperature
- Blood Glucose Concentration.
- Salt Concentration.
- pH.
- Water Potential
Negative feedback systems
Maintain an optimal internal state in the context of a dynamic equilibrium
What controls thermoregulation
Hypothalamus
What are the 2 thermoregulatory centres in the hypothalamus and where are they located?
Heat Loss Centre - in the anterior hypothalamus. This detects a rise in temperature.
Heat Gain Centre - in the posterior hypothalamus. This detects a fall in temperature
Vasodilation
Controlled by heat loss centre and parasympathetic nerves, which cause smooth muscle in skin arterioles to relax.
- Shunt vessels constrict, increasing blood flow to surface capillaries leading to dilation of capillaries, so more heat is lost from the skin by radiation
What occurs as a result of the heat loss centre during an increase in temperature?
Vasodilation, increased sweating, decreased metabolic activity, body hairs flatten and various behavioural responses.
Vasoconstriction
- Sympathetic nerves send impulses causing smooth muscle in the skin arterioles to contract.
- Shunt vessels dilate, diverting blood from capillaries.
- Blood flow to surface capillaries is restricted, so less heat is lost from skin by radiation.
- Reduced blood flow decreases temp of body surface.
What occurs as a result of the heat gain centre during an increase in temperature?
Vasoconstriction, increased metabolic activity, piloerection and various behavioural responses.
Increased metabolic rate occurances when temperature decreases
- Brown fat cells respire a lot more.
- The hormones: Adrenalin and Thyroxine stimulate an increase in metabolism.
- Adrenaline is rapid and short-lived effect
- Thyroxine is slower but longer lasting.
Piloerection
Contraction of erector pili muscles causes body hairs to raise trapping an insulating layer reducing heat loss by radiation & convection. Negligible effect in humans.
Blood vessels supplying liver
Hepatic portal vein - from intestines, carries digested food products (glucose,aminoacids)
Hepatic artery - from aorta, carries oxygenated blood
Transamination
Amino group from one amino acid can be transferred to a different keto-acid to produce a new amino acid.
Deamination
Involves enzymatic removal of NH2 from amino acid along with H to form ammonia NH3 and a keto-acid. Can enter respiratory pathway to release energy via glycolysis or Krebs cycle
What happens to the products of deamination?
NH3 combines with CO2 to form urea and is expelled as urine.
Keto acid is either used in respiration or converted into a carbohydrate and stored as glycogen in the liver.
What does insulin do?
Increases permeability of cells to glucose, increasing its uptake from the blood.
Stimulates glycogen synthase causing glycogenesis and inhibits glucose phosphorylase.
Stimulates conversion of glucose to fats and proteins
Beta cells in islets of langerhans
Cells in pancreas, secrete insulin when blood glucose level rises.
What occurs to glucose in the liver following a rise in blood glucose?
Uses glucose and other substrates in glycolysis and aerobic respiration.
Glycogenesis
Glycogenesis
Conversion of glucose to glycogen
Alpha cells in islets of langerhans
Cells in pancreas, secrete glucagon when blood glucose level lowers.
What occurs during a decrease in blood glucose?
Pancreas detects this and releases glucagon which stimulates glycogenolysis or gluconeogenesis in extreme conditions.
Gluconeogenesis
Conversion of amino acids, fatty acids and glycerol into glucose in the liver and other tissue when blood glucose levels are extremely low.
Glycogenolysis
Breakdown of glycogen into glucose when blood glucose is low.
Hypoglyceamea
When blood glucose falls too low
- Sweating, trembling, blurred vision, poor concentration, can result in fit and a coma
Hyperglyceamia
When blood glucose is too high
- Sickness, drowsiness, stomach pains, can be coma
Type 1 Diabetes
Caused by loss of ß cells, meaning insulin can’t be produced. Managed by diet and insulin injection.
It affects mainly children and young adults.
Males and Females are equally affected
Type 2 Diabetes
Caused by tissues becoming less sensitive to insulin in the circulation. Managed by diet, symptoms decrease w/ weight loss.
Affects mainly older people (40-55), who are overweight and more women than men.
Osmoregulation
Maintaining the water potential of the blood within restricted limits. Osmoreceptors are in the hypothalamus.
Ultrafiltration
Occurs between glomerulus and bowmans capsule forming the glomerular filtrate which is forced out due to high blood pressure from the left ventricle and due to the difference in arteriole size between the afferent and efferent.
Cells forming the filter in the renal corpuscle
- Endothelial cells of capillary have pores allowing plasma to enter. Cells are attached to basement membrane which acts a fine filter.
- Podocytes are of the bowmans capsule which allow filtrate to rapidly pass through.
Adaptations of cells lining the proximal convoluted tubule
- microvilli: large surface area .
- numerous mitochondria: active transport
- carrier proteins: active transport
Antidiuretic hormone
Released by posterior pituitary gland. Attaches to receptors on DCT and collecting duct cells, stimulating aquaporins to move onto cell surfaces.
Aquaporins
Water protein channels which go on surface of DCT and collecting duct, stimulated by ADH.
Decrease in water potential of the blood
- Osmoreceptors in the hypothalamus are stimulated.
- Producing ADH which goes to posterior pituitary gland.
- Is released into blood and increases permeability of distal tubule and collecting duct.
- More water reabsorbed from filtrate, leading smaller volume of more concentrated urine.
- Water potential returns to normal. Osmoreceptors inhibit ADH secretion due to negative feedback
Increase in water potential of the blood
- Stimulation of osmoreceptors is reduced.
- Less ADH released into blood and permeability of distal tubule and collecting ducts is reduced.
- Less water reabsorbed from filtrate, leading to larger volume of more dilute urine.
- Water potential decreases to normal. Osmoreceptors regulate ADH secretion due to negative feedback
Diabetes insipidus
Results in the production of large volumes of dilute urine (diuresis), acute thirst and dehydration.
Can be due to a lack of ADH or lots of alcohol.
Endometrium
Uterus lining
FSH
- Causes growth and development of a Graafian follicle
- Stimulates secretion of Oestrogen from Graafian follicle
LH
- Causes ovulation 14 days (secondary oocyte released).
- Stimulates development of corpus luteum, produced from ruptured follicle. Remains in ovary following ovulation.
- Stimulates corpus luteum to release progesterone & some oestrogen
Oestrogen
- Stimulates repair & proliferation of uterine lining after menstruation. At low levels inhibits FSH & LH produce.
- Peak has positive feedback on FSH causing small surge in concentration at ovulation.
- As conc. rises, LH released from pituitary gland.
Progesterone
- Stimulates proliferation & development of uterine lining in preparation for ovum fertilization.
- Progesterone & oestrogen inhibit FSH preventing any more ova developing during the cycle.
- High levels inhibit LH & its own production, neg. feed.
If fertilisation does not occur
Progesterone level falls, resulting in menstruation & beginning of a new cycle as FSH secretion is no longer inhibited. Corpus luteum in ovary degenerates as LH secretion has been inhibited.
Fertilization
Fusion of sperm and egg to form zygote.
Zona pellucida
Thick membrane surrounding ovum prior to implantation. Secreted by granulosa cells. Has receptors to which sperm heads bind.
Thickens and hardens, and loses receptors after sperm.
Sperms entrance into secondary oocyte
Binds to zona pellucida, then acrosomal enzyme digests path through to surface membrane of secondary oocyte.
Sperm fuses with microvilli and enters cytoplasm
Sperm nucleus swells due to chromatin unravelling
Blastocyst
Stage of fertilization, blastocoel fills w/ liquid from oviduct. Trophoblast thickens at one point to form the inner cell mass.
Trophoblast
Outer layer of blastomeres on zygote
Blastomeres
Smaller cells formed by cleavage of newly fertilised ovum.
Cleavage
Cell division of a fertilised ovum
Blastocoel
Central cavity of hollow ball of blastomeres. Fills with liquid from the oviduct.
If fertilisation occurs
Zygote develops into ball of cells (blastocyst) which embeds itself into uterus wall within 8 days of ovulation
Implantation
Trophoblast cells multiply in presence of endometrium nutrients nutrients and after fertilisation, the blastocyst becomes embedded within the endometrium
When the blastocyst arrives in the uterus
Zona pellucida gradually disappears over about two days, allowing cells of trophoblast to make contact with cells of the endometrium.
Chorion
Outer layer of cells of trophoblast. Form chorionic villi which extend into endometrium.
Fetal component of placenta
Cells of chorion which produce projections called chorionic villi, increase SA. Villi become invaded by branches of two blood vessels of the fetus, the umbilical artery and vein.
- Capillary networks form inside villi. Blood vessels run between fetus & uterus wall in umbilical cord
Umbilical cord
Tough structure, 40cm long, covered in amnion and chorion cells.
Umbillical vein and artery run through it in between foetus and uterus wall.
