Option H: Further Human Physiology

1. Option H: Further Human Physiology IB Biology

2. H1 - Hormonal Control • Hormones = chemical messengers secreted by endocrine glands into the blood and transported to specific target cells. Example: insulin – produced by pancreas; target: liver cells • Hormones can be: • Steroids: progesterone, estrogen, testosterone • Peptide derivative: insulin; leptin (appetite control-metabolism regulation / target = hypothalamus) • Tyrosine derivatives: thyroxine (thyroid hormone) = regulates metabolism

3. Hormone Absorption Different hormones = difference in solubility • Steroid hormones = can cross plasma membrane/nuclear membrane – bind with receptor, affecting gene expression directly • Protein hormones = cannot cross the membrane = trigger a cascade reaction mediated my chemicals called second messengers. Ex: adrenalin = attaches to membrane receptor = stimulates transformation from glycogen to glucose

4. Hypothalamus/Pituitary • - Hypothalamus:Links nervous and endocrine systems(Pituitary: double lobed gland below hypothalamus) •  Hypothalamus controls each lobe differently: • Hypothalamus neurons produce hormones that are transported and stored in vesicles in the axon located in the posterior pituitary. Nerve impulses cause the release of the vesicles into blood stream. • Hypothalamus also produces GnRH (gonadotropin releasing hormone) = transported to anterior pituitary by portal vein = GnRH stimulates production of FSH (follicle stimulating hormone) and LH (luteinizing hormone) by anterior pituitary (target tissue)

6. Integration between pituitary and hypothalamus:ADH • hypothalamus neurosecretory cells produce ADH (anti-diuretic hormone or vasopressin = promotes osmoregulation) • ADH is transported through nerve impulses by to the posterior pituitary where it is stored • Osmoregulatory sensitive cells in the hypothalamus sense changes in solute concentration • ADH is released from its storage region and secreted into the blood • target tissue = collecting ducts of kidney = makes it more permeable to H20 = the body reabsorbs more H20, diluting blood solutes = OSMOREGULATION

7. H2 - Digestion • Digestive juices are secreted into the alimentary canal (lumen of gut) by GLANDS. • Exocrine Glands + juice content: • salivary glands = saliva: amylase, lipase, mucus, slightly alkaline solution that moistens the food, • gastric glands in stomach wall = gastric juice: pepsin, hydrochloric acid, salt, water, mucus • pancreas = pancreatic juice: amylases, trypsin, chymotrypsin, lipase, carboxipeptidase, bicarbonate ion • small intestine = enteric juice: carbohydrases, dipeptidases, enterokinases (enteropeptidases)

8. Pancreas – An exocrine and endocrine gland

9. Exocrine Glands • release secretion into ducts which open onto cavities like skin, mouth, alimentary canal • acini (acinus = singular – “berry”) = cluster of secretory cells • 2 portions: glandular + duct • Exocrine cells have: rough endoplasmic reticulum (b) well developed next to nucleus (c) and Golgi apparatus (d), more secretory vesicles with protein, more mitochondria (a)

10. Gastric Juice Regulation • sight/smell of food = reflex = gastric juices released • How? • presence of food in stomach = secretion of gastrin by endocrine cells within the stomach wall → target tissue: gastric juice cells in stomach • gastrin: polypeptide hormone produced by mucous lining of stomach • stimulates HCl production (parietal cells) and pepsinogen production (chief cells) • when pH in stomach drops = gastrin secretion is inhibited by secretin (duodenum secretion) • Membrane-bound enzymes in the gut epithelium • enzyme is attached to fixed surface = more efficient = not removed/plays other roles too • examples of membrane bound enzymes = enterokinase, maltase, lactase, sucrase

11. Cellulose • humans lack cellulase • cellulose remains undigested/released in feces • cows/sheep = symbiotic relationship with cellulose digesting bacteria (termites/protozoan too) • cellulose = fiber = creates bulk (mass) = stimulates peristalsis/satiety

12. Digestive Enzymes • Pepsin/Trypsin = proteases • Pepsinogen (stomach) + Trypsinogen (pancreas) = zymogens = inactive enzyme precursor chemically altered after secretion to become active (this prevents self digestion of the cell)

13. Ulcers/Cancer in the stomach • acidic environment = barrier to infections • mucus protects stomach wall • Helicobacter pylori (bacterium) cause stomach infection leading to ulcers → can lead to cancer Lipid Digestion • Lipase – water soluble enzyme – acts on water-insoluble lipids (tend to coalesce into larger droplets) = PROBLEM • Triglycerides turn into fatty acids and glycerol • Bile acts as “detergent” = breaks fat into tiny droplets (emulsion), increasing surface area exposed to lipase

14. H3 - Absorption of Digested Food • Structure of ileum: • villi = fingerlike projections that increase surface area of small intestine • crypts = contain secretory cells of intestinal secretion • mucosa = mucus secreting membrane • muscles = create contractions – promote movement of chyme along alimentary canal • serosa = tough outer membrane composed of collagen • Unabsorbed material / eliminated with feces (egested) = cellulose, lignin, bile pigments, bacteria and intestinal cells

16. Absorption in the small intestine • absorption happens through epithelial cells covering each villus • nutrients must cross epithelial cells (not enough space to go between cells = tight junctions) • cell membrane = microvilli = increase surface area even more • cell uses ATP to make endocytosis happen (cell needs many mitochondria for that) • Transport in the intestine can involve: • Simple diffusion (molecules follow concentration gradient, crossing the membrane through channel proteins – “pore”) • Facilitated diffusion (ex. Fructose) • Active transport (ex. Glucose = pumps use energy to move nutrient against concentration gradient) • Endocytosis (pynocytosis = cells uses energy = vesicles carry substances)

17. Absorption of fatty acids • monoglycerides, bile salts, fatty acids = combine forming micelles → diffuse across membrane → inside cell they reassemble into triglycerides • protein is added to lipid → vesicles called chylomicrons • exocytosis → release lipoprotein from cell → enter lacteals vessels (lymphatic system) → converge into lymph vessels that carry them to circulatory system