XABY04 PHYSIOLOGY

• Homeostasis is the maintenance of a constant internal environment
• Anterior hypothalamus contains the heat loss centre and is responsible for detecting rises in temperature
• Posterior hypothalamus is the heat gain centre and detects falls in temperature
• Vasodilation (INCREASE in temp)

  • nerve impulses in parasympathetic from hypothalamus cause smooth muscle in skin arterioles to relax
  • shunt vessels constrict - blood flow increases to capillaries leading to dilation
  • more heat lost
• Increased sweating (INCREASE in temp)

  • sweat glands remove water and secrete onto skin surface
  • body heat evaporates producing a cooling effect
• Decreased metabolic activity (INCREASE in temp)

  • reduced heat production by respiration
• What happens when there is an INCREASE in temperature?

  1. vasodilation
  2. increased sweating
  3. decreased metabolic activity
  4. no shivering
  5. flattened body hair - decrease insulating layer of skin
  6. behavioural responses - shade, laying down, removing clothes
• Vasoconstriction (DECREASE in temp)

  • nerve impulse in sympathetic nerves in hypothalamus cause smooth muscle in skin arteriole to contract
  • shunt vessels dilate - divert blood flow away from capillaries
  • less heat loss from skin as blood flow to skin is restricted
  • temperature of body surface DECREASED
• INCREASED metabolic rate (DECREASE in temp)

  • increased metabolic activity - respiration in brown fat cells to generate heat
  • adrenaline and thyroxine secreted to stimulate increase in metabolic rate
  • adrenaline - faster action, short lived effect
  • thryroxine - slower action, long lived effect
• What happens when there is a DECREASE in temp?

  1. vasoconstriction
  2. increased metabolic rate
  3. shivering - involuntary muscle contraction
  4. piloerection - erector pili muscles contract causing body hairs to rise trapping an insulating layer
  5. no sweating
  6. behavioural responses - huddling together, sunny areas, more clothes
• Hepatic portal vein - supplies blood with high concentrations of digested food products (e.g glucose and amino acids)
• Hepatic artery - supplies oxygenated blood
• Functions of the liver

  1. transamination - NH2 group from one amino acid can be transferred to another keto acid to make a new amino acid
  2. deamination - enzymatic removal of NH2 along with hydrogen to form NH3
• Deamination

  • NH3 and keto acid produced can enter the respiratory cycle to release energy via glycolysis or the kreb's cycle
  • NH3 is highly toxic and combines with CO2 in the ornithine cycle to make urea
  • urea - soluble and excreted in urine, keto acid - used in respiration or converted to carbohydrate and stored as glycogen in the liver
• INCREASE in blood glucose

  1. detected by pancreas which secretes insulin from beta cells into the bloodstream
  2. insulin stimulates liver to increase permeability to glucose
  3. glucose and other substrates e.g glycerol and amino acids in glycolysis and aerobic respiration
  4. excess glucose converted to glycogen (glycogenesis) - glycogen synthase active, glycogen phosphorylase inactive
  5. stimulated glucose conversion into fats and proteins
• DECREASE in blood glucose

  1. detected by pancreas which secretes glucagon from alpha cells into the bloodstream
  2. glucagon stimulates the breakdown of glycogen to glucose via enzymes (glycogenolysis)
• Adrenaline has a similar action to glucagon

  • acts in muscle where it stimulates glycogenolysis
  • the glucose phosphate it releases cannot be released to increase blood glucose
  • supplies glucose for immediate use in glycolysis by muscles only
•  HYPOGLYCAEMIA - blood glucose drops too low

  • sweating, trembling, blurred vision, poor concentration
  • untreated can lead to a fit or a coma
• HYPERGLYCAEMIA - blood glucose rises too high

  • sickness, drowsiness, stomach pain
  • untreated can lead to a coma
• TYPE 1 DIABETES - loss of beta cells and so insulin isn't produced

  • managed by diet (low sugar) and insulin injections
  • affects mainly children and young adults
  • males and females equally affected
  • 5-10% of the total number of diabetics
• TYPE 2 DIABETES - tissues becoming insulin resistant

  • managed by diet and losing weight
  • mainly older people 40-55
  • usually overweight people
  • women rather than men
• GESTATIONAL DIABETES

  • caused by pregnancy and disappears after childbirth
  • glucose in urine, high blood pressure towards the end of pregnancy
• How to diagnose a diabetic?

  • glucose cannot be recovered from the filtrate
  • glucose appears in the urine
• Osmoregulation - maintaining the water potential of the blood within restricted limits
• Function of the kidney

  • filter the blood (ultrafiltration)
  • selectively reabsorb useful substances e.g glucose, amino acids, water
• What does the cortex (outer part) of the kidney contain?

  1. glomerulus
  2. bowman's capsule
  3. proximal and distal convoluted tubule
• What does the medulla (inner part) of the kidney contain?

  1. loop of Henle
  2. collecting duct
• How is the glomerular filtrate formed?

  1. High blood pressure from the left ventricle forces filtrate out of the glomerulus into bowman's capsule

  2. Afferent arteriole is wider than efferent arteriole causing even higher blood pressure

  3. Pores in the endothelial cells of capillaries allow plasma through but hold back blood cells

  4. Basement membrane is attached and holds back large plasma proteins in the plasma

  5. Only water, glucose, amino acids, ions, urea pass through

  6. Epithelium cells (podocytes) of bowman's capsule have 'feet-like' structures that extend to the basement membrane and allow filtrate to pass through
• How does selective reabsorption work?

  1. blood cells, large plasma proteins and some of the water remain in the blood capillary and enter the efferent arteriole
  2. each efferent arteriole form a capillary network around the rest of each nephron
  3. useful substances from the filtrate are selectively reabsorbed
  4. filtered blood eventually leaves via the renal vein
• What are the main adaptations of the PCT?

  1. microvilli - large surface area
  2. numerous mitochondria to provide ATP - active transport
  3. carrier proteins in the cell surface membranes - active transport
• What is the role of the loop of Henle?

  • concentration gradient of sodium and chloride ions is created in the medulla
  • the concentrations increase deeper down the medulla
  • a water potential is created down the medulla - lower at the base, deeper in the medullary tissue
  • more water can be reabsorbed by the collecting duct from the filtrate by osmosis
• How is the increase in Na and Cl concentration created by the loop of Henle?

  1. descending limb permeable to water but not to Na+/Cl- so some water leaves by osmosis into tissue fluid of medulla then enters surrounding blood capillaries
  2. ion conc in filtrate at base of L.O.H increases; Na+/Cl- move from ascending limb into medulla via diffusion
  3. cells in upper part of ascending limb actively transport Na+/Cl- from filtrate into surrounding tissue
  4. ascending limb impermeable to water - increased water potential in filtrate and decreased water potential in tissue fluid of medulla
• Aquaporins - water protein channels that enable more water to be reabsorbed from these structures by osmosis down a water potential gradient
• Water reabsorption in the DCT and collecting duct

  • water that leaves the DCT and CD passes into medullary tissue and then to blood capillaries that join to the renal vein
  • high conc of Na+/Cl- down the medulla makes sure there is always a lower water potential in the medulla - more water can be reabsorbed
  • the amount of water depends on the water potential of the blood
• The response to a decrease in blood water potential

  1. osmoreceptors in hypothalamus stimulated
  2. more ADH produced and travels to posterior pituitary gland
  3. more ADH released into blood by posterior pituituary gland
  4. DCT and collecting duct more permeable
  5. more water reabsorbed from the filtrate by osmosis
  6. less water in urine and smaller, more concentrated urine
• The response to an increase in water potential of blood

  1. osmoreceptors less stimulated
  2. less ADH released into blood and DCT and collecting duct less permeable
  3. less water reabsorbed from filtrate back into blood
  4. more urine and larger, more dilute
  5. water potential decreases back to normal