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Option H: Further Human
Physiology
IB Biology
H1 - Hormonal ControlHormones = 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
Hormone AbsorptionDifferent hormones = difference in solubility
Steroid hormones = can cross plasma membrane/nuclear membrane – bind with receptor, affecting gene expression directlyProtein 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
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)
Integration between pituitary and hypothalamus:
ADHhypothalamus 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 concentrationADH is released from its storage region and secreted into the bloodtarget tissue = collecting ducts of kidney = makes it more permeable to H20 = the body reabsorbs more H20, diluting blood solutes = OSMOREGULATION
H2 - DigestionDigestive 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)
Pancreas – An exocrine and endocrine gland
Exocrine Glandsrelease secretion into ducts which open onto cavities like skin, mouth, alimentary canalacini (acinus = singular – “berry”) = cluster of secretory cells2 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)
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
Cellulosehumans lack cellulase cellulose remains undigested/released in fecescows/sheep = symbiotic relationship with cellulose digesting bacteria (termites/protozoan too)cellulose = fiber = creates bulk (mass) = stimulates peristalsis/satiety
Digestive EnzymesPepsin/Trypsin = proteasesPepsinogen (stomach) + Trypsinogen (pancreas) = zymogens = inactive enzyme precursor chemically altered after secretion to become active (this prevents self digestion of the cell)
Ulcers/Cancer in the stomachacidic environment = barrier to infectionsmucus protects stomach wallHelicobacter pylori (bacterium) cause stomach infection leading to ulcers → can lead to cancer
Lipid DigestionLipase – water soluble enzyme – acts on water-insoluble lipids (tend to coalesce into larger droplets) = PROBLEMTriglycerides turn into fatty acids and glycerolBile acts as “detergent” = breaks fat into tiny droplets (emulsion), increasing surface area exposed to lipase
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
Absorption in the small intestine
absorption happens through epithelial cells covering each villusnutrients must cross epithelial cells (not enough space to go between cells = tight junctions)cell membrane = microvilli = increase surface area even morecell 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)
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
