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.