block 6- the gastrointestinal system Flashcards
what are the two parts of the digestive system
- Digestive Tract
- Accessory Organs (liver, pancreas, gallbladder)
what are the primary regions of the digestive tract in order
Oral cavity (mouth) → Pharynx → Oesophagus → Stomach → Small Intestine → Large Intestine → Rectum/Anus
Continuous passage with different functional chambers.
what are the 4 main layers of the GI tract
inner to outer
- Mucosa (Epithelial lining of lumen, secretes mucus that lubricates and protects the tract)
- Submucosa (Connective tissue layer containing blood vessels, lymph vessels, nerves)
- Muscularis- two layers
-Circular (wraps around)
-Longitudinal (runs along the tract) - Serosa (Secretes fluid for lubrication of outside+inside of GI tract)
Also called Adventitia (when not lubricating externally)
the oral cavity
-Hard Palate (made of bone at the anterior end)
-Soft Palate (made of smooth + skeletal muscle at the posterior end)
-Tonsils (between palatoglossal (PG) & palatopharyngeal (PP) arches)
-Fauces (back of the mouth)
the tongue
-Helps in food breakdown.
-Oral/anterior part (freely movable and is attached to the floor via the lingual frenulum) - makes up 2/3rds
-Posterior/pharyngeal Part (fixed and is connected with hyoid bone, epiglottis and oropharynx)- 1/3rd
-Epiglottis (prevents food entering airway)
the pharnyx
-Passageway for both food and air.
-Lined with moist stratified squamous epithelium to prevent abrasion.
three regions:
nasopharynx - nasal cavity to uvulva
oropharynx- uvulva to epiglottis
laryngopharynx- epiglottis to oesophagus
the oesophagus
-Expandable to accommodate food volume.
-muscular tube with a outer longitudinal and inner circular layer
-Passes through diaphragm via three openings.
-Sphincters(thickenings) at both entrances and exits to control swallowing speed.
-Regulates food entry into the GI tract.
- moist stratified squamous epithelium
- passes from thoracic cavity into the abdominal cavity through an opening in the diaphagm (T10-oesophageal hiatus)
the stomach
-Food Entry: Controlled by Cardiac Sphincter
-Food Exit: Controlled by Pyloric Sphincter
-Rugae (Folds): Allow stomach expansion
-Environment: Highly acidic
-Epithelium: Simple Columnar
-Gastric Glands: Secrete digestive substances
3 main regions;
1. fundus
2. body
3. pyloric region
what are the 3 layers of stomach muscles
- Outer Longitudinal (secretes serosa fluid to lubricate)
- Middle Circular
- Inner Oblique (extra twisting motion)
the peritoneum
Peritoneum: continuous sheets of serous membrane that supports & anchors the stomach
.
Retroperitoneal Space: Behind the stomach, near the spine.
intraperitoneal - inside the peritoneum
parietal peritoneum = lines the abdominal and pelvic cavities
visceral peritoneum = covers most abdominal organs
peritoneal cavity = space between the two perinoteums
what are mesentries
- are peritoneal folds that connect organs to each other or the abdominal wall
- keeping everything in place
the small intestine
Held in place by mesentery.
- where nutrient absorption occurs
Divisions:
1. Duodenum
Brunner’s glands secrete alkaline mucus
30cm
extends from pyloric sphincter to jejunum
c shaped structure
short superior region
descending part containing major and minor duodenal papillae
- Jejunum
- 2.5m
- is completely peritonised (covered in peritoneum)
- extends from duodenojejunal flexture to ileum - Ileum
contains Peyer’s patches to monitor bacteria concentrations
3.5m
completely peritonised
extends from the jejunum to the large intestine to the ileocecal junction
Structural Features for Absorption:
Villi (increase surface area)
Lacteals (absorb fats)
Goblet Cells (secrete mucus)
Cell Types: Do not produce HCl, but some migrate along the villi.
the 4 types of cells produced in the intestinal glands
- absorptive - digestive enzymes
- goblet - mucus
- granular or paneth -lyzozyme
- endocrine - hormones
- the absorptive and goblet migrate to cover villi surface
- the granular and endocrine remain in the bottom
- villi are covered with simple columnar epithelium and contain a blood capillary network and lymphatic capillary
the large intestine
Functions:
Reabsorbs water
Compacts waste into faeces
Absorbs vitamins
Houses 700+ species of bacteria
Stores faecal material
Structure:
Extends from Ileocecal Valve to Anus
Wider diameter than the small intestine
First Part: Cecum (with appendix)
Main Cells: Goblet cells (secrete mucus) and others cells are absorptive and granular
Muscle Features:
Taeniae coli: Longitudinal muscle band running down the middle
serosa containing fat-filled pouches: Unknown function
colons:
ascending
descending
transverse
sigmoid
the rectum and anal canal
Rectum:
-Located below the pelvis
-Thicker muscular layers
-has transverse rectal folds (valves)
rectal mucosa of simple columnar epithelium with tubular glands and lots of goblet cells
Anal Canal (Final 3 cm):
Superior Part: Simple columnar epithelium arranged in longitudnal folds and anal columns where arteries and veins are
Anal Columns: Provide extra lubrication
Sphincters:
Internal (smooth muscle) – Involuntary
External (skeletal muscle) – Voluntary
what are the major sphincters of the GI tract
- thickenings of the inner circular muscle layer(muscularis) along the tract give rise to sphincters and valves
- Upper Oesophageal Sphincter – Controls food entry into oesophagus.
- Lower Oesophageal (Cardiac) Sphincter – Prevents reflux into oesophagus.
- Pyloric Sphincter – Regulates food entry into the small intestine.
- Ileocecal Valve – Controls movement from the small to the large intestine.
- Internal Anal Sphincter – Involuntary control.
- External Anal Sphincter – Voluntary control.
what are the boundaries of the oral cavity
- lips anteriorly
- cheeks laterally
- palate superiorly
- tongue inferiorly
Digestive System Functions of Secretions
- Chemical Digestion: Breaks down food into smaller components.
- Lubrication: Ensures smooth movement of food through the digestive tract without causing damage.
- Signaling: Allows communication between different parts of the digestive system to coordinate functions.
- Protection: Protects against pathogens and injury.
- Activation of Enzymes: Enzymes are activated to assist in digestion.
- Excretion of Waste: Removal of undigested substances or toxins.
definitions of exocrine and endocrine
Endocrine: Secretion of substances (e.g., hormones) into the bloodstream.
Exocrine: Secretion of substances through ducts to the surface or outside the body (e.g., digestive enzymes).
explain the secretion of the salivary gland
Major Glands: 3 pairs of exocrine glands that secrete salivia via a duct (parotid, submandibular, sublingual).
Minor Glands: 600-1000 glands scattered in the oral cavity.
- each one is an exocrine gland with it’s own duct, carrying secretions from the gland to the mouth
describe the composition of salivia
99.4% water, the remaining 0.6% composed of:
Mucins: Provide viscosity for lubrication and protection.
Electrolytes: Help with osmotic balance and act as buffers to keep pH at 7.
Antibodies: Defend against pathogens.
Enzymes: Initiate chemical breakdown (e.g., amylase).
Xerostomia (Dry Mouth): Can cause tooth decay, infection, dysphagia (swallowing problems), and other symptoms.
explain the gastric secretions of the stomach
Components of Gastric Juice:(aid stomach functions)
-Water
-Hydrochloric Acid (HCl): Lowers pH to activate enzymes and kill microbes.
-Pepsinogen: Inactive form of pepsin (activated at low pH to break down proteins).
-Intrinsic Factor: Essential for Vitamin B12 absorption.
-Mucus: Protects the stomach lining.
Activation of Pepsin: Pepsinogen is activated to pepsin at pH < 3.
describe the gastric gland cells
- parietal cells
- secrete intrinsic factors
- needed for the absorption of vitamin B12
- secretes HCL to kill microbes, activate enzymes and denature proteins - chief cells
- secrete pepsinogen
-converted to pepsin - active form
secretes gastric lipase - spilts short chain triglycerides into fatty acids and monoglycerides - mucous cells
- secrete mucus
explain exocrine pancreatic secretions
pancreas
Exocrine Secretions :(98% of cells)
-Alkaline Fluid: Neutralizes stomach acid.
- 1.2-1.5L of pancreatic juice/day
Enzymes (e.g., Trypsinogen): Activated by bile and are essential for protein digestion.
Acinar Cells: Secrete digestive enzymes.
describe the pancreatic enzymes
pancreatic amylase - digests starch
pancreatic lipase - digests fat
ribonucleoase - digests RNA
deoxyribonclease - digests DNA
-amylase, lipase and nucleases are secreted in active form but require ions or bile for optimal activity
- proteases secreted in inactive form and activated by the duodenum
- trypsinogen is activated to trypsin by brush border enzyme enteropeptidase
- procarboxypepidase and chymotrypsinogen are activated by trypsin
describe endocrine pancreatic secretions
- Insulin, glucagon (regulate glucose homeostasis).
- the other 2%
- a cells secrete glucagon in response to a fall in blood glucose
- this stimulates glycogenolysis and gluconeogenesis
- b cells secrete insulin in response to a rise in blood glucose
- this is inhibited by adrenaline in acute stress
- allows cells to utilise glucose
- 8 cells secrete somatostatin which is stimulated by cholinergic innervation
- inhibits gastrin release
liver and gallbladder secretion
Bile:
-Produced by hepatocytes (liver cells) and stored in the gallbladder.
-Composition: Bile salts, bilirubin, cholesterol, phospholipids, electrolytes.
-bile is secreted into bile canaliculi then bile ductules then the bile ducts
Functions:
-Aids in lipid digestion (emulsifies fats).
-Neutralizes stomach acid providing optimum pH for enzymes
-Excretes waste products (e.g., bilirubin).
-Bile Release: Triggered by food intake, stored bile is released into the small intestine.
the gallbladder
- is a thin walled, pear shaped muscular sac on the ventral surface of the liver
- stores and concentrates bile by absorbing its water and ions
- releases ble via the cystic duct, which flows into the bile duct
describe intestinal secretions
Mucus: Protects the intestinal lining and lubricates food for smoother passage.
Watery Secretions: Aid digestion and absorption.
explain the regulation of gastric secretions
- Cephalic Phase (Preparation)
-Triggered by sight, smell, taste, or thought of food.
-CNS Activation: Signals salivary and gastric glands to prepare for food.
-Facial, glossopharyngeal and vagus nerves are activated (cranial) - Gastric Phase (Food in the Stomach)
-Stimulation: Distension of the stomach and increased pH activate stretch receptors and chemoreceptors.
-Response: Peristalsis and gastric juice secretion to break down food.
-Negative Feedback: When food moves to the duodenum, it decreases gastric secretion. - Intestinal Phase (Food in the Small Intestine)
-Inhibition: Prevents more food from entering the stomach and slows gastric motility.
-Hormones Involved:
Cholecystokinin (CCK): Inhibits gastric secretions and motility.
Secretin: Stimulates pancreatic secretions and inhibits gastric acid.
Enterogastric Reflex: Neural feedback that slows gastric emptying.
overview of digestion
Ingestion: Taking in food.
Digestion: Breakdown of food into absorbable nutrients.
Absorption: Nutrients are absorbed through the intestinal lining into the bloodstream.
Excretion: Undigested materials and waste are eliminated from the body.
primary vs secondary active transport
primary = Active transport directly uses energy (usually ATP) to move molecules against their concentration gradient through a carrier protein.
secondary = Does not directly use ATP but relies on the electrochemical gradient created by primary active transport. It uses the energy stored in the gradient of one molecule (e.g., sodium) to move another molecule against its concentration gradient. (a co-transporter)
digestion and absorption of carbohydrates
Types of Carbohydrates:
1. Polysaccharides: Long chains of monosaccharides that can be digestible or non digestible (e.g., starch made of glucose). Found in rice, pasta
2. Sugars: Shorter chains, such as monosaccharides and disaccharides. Found in fruits, vegetables, dairy, etc.
Enzymes Involved in Digestion:
Lactase: Breaks down lactose into glucose and galactose.
Amylase: Breaks down starch into smaller sugars.
Absorption:
Fructose: Absorbed via facilitated diffusion.
Glucose & Galactose: Absorbed via secondary active transport using the sodium gradient.
Energy is required for absorption.
These monosaccharides are absorbed at the brush border to avoid bacterial use of nutrients in the small intestine.
what enzymes can break down carbs?
mouth -> salivary amylase: breaks down starch to maltose
pancreas -> pancreatic amylase: breaks down starch to maltose
small intestine microvilli -> specific oligosaccharides: produce monosaccharides
Which monosaccharide(s) require(s) energy for absorption?
Galactose and glucose
proteins (amino acids and peptides)
Digestion:
Broken down into smaller peptides and amino acids by enzymes (e.g., pepsin, trypsin).
Absorption:
Small Peptides (up to 3 amino acids): Absorbed via secondary active transport.
Amino Acids: Absorbed via facilitated diffusion or secondary active transport.
name the enzymes that can break down proteins
stomach -> pepsin: produces smaller polypeptide chains
pancreas -> trypsin, chymotrypsin, carboxypeptidase: produce smaller peptide chains
small intestine microvilli -> specific peptidases: produces tripeptides, dipeptides and amino acids
lipids
types of Lipids: Triglycerides, phospholipids, cholesterol, fat-soluble vitamins.
Digestion:
Lipase: Breaks triglycerides into monoglycerides and fatty acids.
Emulsification:
Lipid droplets are broken down into smaller droplets by bile salts and stomach churning to increase surface area.
Absorption:
Fatty acids and monoglycerides are absorbed into enterocytes and recombined into triglycerides.
Chylomicrons are formed (contain triglycerides, cholesterol, phospholipids, and proteins).
Chylomicrons enter lymphatic vessels (lacteals) as they are too large to enter blood vessels.
Why do chylomicrons enter lymph rather than blood?
too large to enter blood as cannot pass through capillary wall
- Lymphatic capillaries lack basement membrane and are more permeable to large particles
vitamins
Fat-Soluble Vitamins (A, D, E, K): Absorbed with lipids via micelles.
Water-Soluble Vitamins (C, B, B12): Absorbed by passive or active transport.
Vitamin B12: Requires intrinsic factor for absorption via endocytosis.
In the Large Intestine: Vitamin K and B vitamins from bacterial metabolism are absorbed.
- vitamins are organic substances that cannot be manufactured by the body
how could a blockage of the bile duct lead to vitamin E deficiency?
=vitamin E is fat soluble so must be carried via a micelle
Bile duct delivers bile to SI to allow micelle generation
electrolytes and minerals
Electrolyte Absorption:
Iron: Absorbed by divalent metal-ion transporter 1.
Calcium: Absorption regulated by vitamin D and parathyroid hormone.
Sodium (Na+): Absorbed with glucose and amino acids.
Potassium (K+): Absorbed via passive diffusion in response to osmotic gradients.
- occurs mostly along the length of the small intestine
- usually by active transport
water absorption
-Around 9L of fluid is absorbed daily.
95% of water is absorbed in the small intestine by osmosis.
-Water absorption is coupled with solute absorption to maintain osmotic gradients.
what is malabsorption
= any condition that prevents us absorbing nutrients into the body
causes:
- interference of delievry of bile or pancreatic juice
- damaged intestinal mucosa
- Gluten-sensitive enteropathy- condition affecting intestines (celiac disease)
- Gluten damages the intestinal villi and brush border
– Treated by eliminating gluten from the diet
enzymes that break lipids down into smaller units
mouth -> lingual lipase: digests <10% of lipid
stomach -> gastric lipase: small amount
pancreas -> pancreatic lipase: majority of lipids
fat emulsification steps
- large fat globules are emulsified(physically broken up into smaller fat droplets) by bile salts in the duodenum
- digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides. these then associate with bile salts to form micelles.
- fatty acids and monoglycerides leave micelles and diffuse into epithelial cells where they are recombined and packaged with other lipoid substances and proteins to form chylomicrons
- chylomicrons are extruded from the epithelial cells by exocytosis. the chylomicrons then enter lacteals. they are carried away from the intestine by lymph.
explain the different transport mechanisms
Simple Diffusion: Movement of non-polar, small molecules (e.g., oxygen) across the membrane.
Facilitated Diffusion: Movement of larger or charged molecules (e.g., glucose, sodium) through specific transport proteins.
Active Transport:
Primary Active Transport: Direct energy use via a carrier protein (e.g., sodium-potassium pump).
Secondary Active Transport: Uses the concentration gradient of one substance (e.g., sodium) to transport another (e.g., glucose).
the anatomy of the liver
-Largest internal organ (~1.5 kg), in the upper right quadrant of the abdomen.
-Protected by the rib cage, located under the diaphragm.
lobes:
-Right (larger) & Left (smaller), separated by falciform ligament.
-Quadrate (top) & Caudate (bottom) lobes (part of the right lobe).
the blood supply of the liver
dual blood supply
-Hepatic artery (oxygen-rich blood) from the celiac trunk of aorta.
- smaller
-Hepatic portal vein (nutrient-rich, deoxygenated blood) from the GI tract.
- main supply
venous drainage of the liver
- Once blood has passed through the liver it is drained into the inferior vena cava by 3 hepatic veins
- Left hepatic vein supplies left lobe
- Right hepatic vein to right lobe
- Middle hepatic vein to central region
what is the porta hepatis and the portial triad
- the portal hepatis is the main site where structures enter and leave the liver including portal triad, nerves and lymphatics
portal triad consists of:
- hepatic artery and vein which bring nutrients to the liver
- the bile duct which leaves the liver
what is the hepatic portal system
- a portal system connects one organ to another without returning to the heart first
- Blood draining from GI tract, pancreas and spleen is carried to the liver first
-
- Blood draining from GI tract, pancreas and spleen is carried to the liver first
describe the histology of the liver
hepatocytes (80% of liver cells) – perform metabolic & detox functions.
Hexagonal lobules: Each has a central vein & portal triad (at each corner).
Sinusoids (specialized capillaries):
-Fenestrated endothelium allows nutrient/metabolite exchange.
-Contain Kupffer cells (macrophages that break down RBCs).
-Bile Canaliculi: Tiny ducts collecting bile from hepatocytes.
what are stellate cells
=sit within plasma within the space of disse
-inactive in healthy individuals
if liver is damaged cell is activated, involved in collagen production and storage of vitamin A
what is a lobule
- made up of different hepatocytes all going towards the central vein
- The hepatocytes and vessels of the liver are arranged in hexagons with branches of the portal triad at each corner and a central vein
what is the space of disse in the liver
is a space between a hepatocyte, and a sinusoid in the liver. It contains the blood plasma.
sinusoids
- blood from the hepatic artery and portal vein enter these specialised capillaries
- they are large, low pressure vessels
- drain the blood it receives into the central vein
functions of the liver
- Metabolism
Carbohydrates: Glycogen storage & breakdown (glucagon vs insulin).
Lipids: Lipoprotein synthesis (for fat transport).
Proteins: Deamination of amino acids → urea cycle (removes toxic ammonia). - Detoxification
- Excretion
Bilirubin excretion (by-product of RBC breakdown). - Storage
Glycogen (carbs), triglycerides (fats), vitamins (A, D, B12), minerals (iron, copper). - Synthesis
Bile salts (for fat digestion).
Plasma proteins (albumin, clotting factors).
Cholesterol, angiotensinogen (blood pressure regulation). - Phagocytosis
Kupffer cells remove old RBCs & pathogens. - Heat Production
High metabolic activity → generates body heat.
detoxification action of the liver
overview of three phases
Phase I (Modification): drug is turned into a metabolite by the addition of reactive and polar groups, this prevents free diffusion across the membranes
Phase II (Conjugation): Makes molecules water-soluble for excretion through the attatchment of an ionised group
Phase III (Excretion): Eliminates via urine (smaller metabolites by kidneys) or bile (larger metabolites by faeces).
drug metabolism phase 1
modification
- Primarily performed by cytochrome P450 enzymes located in smooth endoplasmic reticulum of hepatocytes
Enzymatic incorporation of polar groups (O or OH):
* Oxidation
* Reduction
* Hydrolysis
phase 2- conjugation
Addition of an ionised group:
* Glutathione
* Sulphate
* Glycine
* Glucuronic acid
- occurs in cytoplasm of hepatocytes
- makes metabolite water soluble for trasnport and inactivates it
what is billirubin
- formed from red blood cells breakdown
- broken down by macrophages
-is bound to albumin in plasma for transport - excess billirubin causes jaundice
- free billirubin cab be potentially toxic if it crosses the blood brain barrier
- Bilirubin conjugated to glucuronic acid to form bilirubin glucuronide.
- The conjugated bilirubin is more soluble and can be excreted by the hepatocyte into the biliary canaliculi
billirubin metabolism and jaundice
Bilirubin breakdown: RBCs → Heme → Bilirubin (toxic, must be processed).
Transported to liver bound to albumin, conjugated for excretion in bile.
Neonatal Jaundice: Immature liver lacks enzyme for bilirubin conjugation.
Phototherapy converts bilirubin to a water-soluble form for excretion.
liver regeneration
-Hepatocytes divide to maintain function.
-Severe damage activates liver stem cells.
-Cirrhosis impairs regeneration ability
liver functions- carbohydrate metabolism
= Maintains blood glucose homeostasis by storing or releasing glucose.
- High blood glucose: Insulin stimulates glycogenesis (glucose → glycogen for storage).
- Low blood glucose: Glucagon stimulates glycogenolysis (glycogen → glucose for energy).
- If glycogen stores are depleted, gluconeogenesis occurs (new glucose formed from non-carbs like amino acids).
- maintaining glucose levels is vital as too high levels could lead to impaired nervous system dysfunctiona and too low could lead to complications with diabetes
the process of glucose uptake by the liver
- uptake of glucose via GLUT2 receptors in respose to high glucose levels
-insulin is released from the pancreas - glucose -> glucose-6-phosphate via glucokinase
liver converts G6P -> glycogen via glycogen synthase (glycogenesis) - increased triglyceride synthesis
decreased glucose level response by the liver
- glucagon is released from the pancreas
liver converts glycogen -> glucose-1-phosphate via glycogen phosphorylase (gluconeogenesis) - synthesis of glucose from amino acids and triglycerides
- is a 11 enzyme catalysed reaction
- requires ATP and GTP
liver function - lipid metabolism
-Synthesizes lipoproteins (for fat transport in the blood).
-Stores triglycerides (fat storage).
-Beta-oxidation: Breaks down fatty acids to generate ATP.
-Cholesterol synthesis: Produces cholesterol, some used for bile salt production.
liver function - protein metabolism
-Deamination: Removes amino groups from amino acids → produces ammonia (toxic).
-Urea cycle: Converts toxic ammonia into urea, excreted in urine.
-Synthesizes plasma proteins (albumin, clotting factors).
- synthesises all non-essential amino acids
functions of the kidney
main role = homeostasis
others:
- Waste Disposal – Removes metabolic waste.
Osmoregulation – Maintains fluid and ion balance.
Blood Volume & Pressure Regulation – Adjusts blood volume by controlling water excretion.
Blood pH Regulation – Controls H+ and HCO3- levels.
Hormone Production – Produces hormones like erythropoietin and renin.
anatomy of the renal system
structures and functions
Kidneys – Filter blood, produce urine.
Located retroperitoneally (behind peritoneal cavity) at the level of the 12th rib.
Left kidney higher than right.
Receives 20-25% of cardiac output (~1200ml/min) via renal arteries from the aorta.
- blood returned to inferior vena cava via renal veins
-Ureters – Transport urine from kidneys to bladder.
-Bladder – Stores 700-1000ml of urine.
-Urination involves urethral sphincter relaxation & detrusor muscle contraction.
-Urethra – Allows urine to exit the body.
describe the internal structure of the kidney and the flow of urine
Fibrous Capsule – Protective, non-flexible outer layer.
Cortex – Outer dark brown region.
Medulla – Inner lighter region where urine is formed.
Urine Flow:
Urine flows from medullary region → minor calyx → major calyx → collecting tubules → ureter.
describe the structure and function of the nephron
= Is the functional unit of the kidney.
Consists of:
Renal Corpuscle (in cortex) → Filtration.
Renal Tubule (spans cortex & medulla) → Reabsorption & secretion.
describe the renal corpuscle
- where blood plasma is filtered
composed of:
1. Glomerulus (Capillary Bed) – Where filtration occurs.
2. Bowman’s Capsule – Collects filtrate.
- space between the two layers is the capsular space, where the filtrates flow through
Special Blood Supply:
Capillaries are supplied & drained by arterioles (instead of veins).
Arterioles can constrict/dilate to regulate filtration pressure.
Epithelium Type: Simple squamous (thin for filtration).
Filtration Process:
Allows: Water, sodium, glucose, chloride.
Prevents: RBCs, large proteins.
the renal tubule
reabsorption and secretion
- Proximal Convoluted Tubule (PCT) –
Reabsorbs glucose, sodium, other solutes. - Loop of Henle – Creates osmotic gradient for water/solute exchange (counter-current multiplier).
- Descending limb – Water permeable, solute impermeable.
- Ascending limb – Water impermeable, solute permeable.
- Thick ascending limb – Active transport of sodium/chloride.
- Distal Convoluted Tubule (DCT) – Water reabsorption, drains into collecting duct.
- Collecting Duct – Controls final urine concentration (permeability changes based on hydration).
ultrafiltration
- Glomerular filtration is the first step of urine production
- Water and most solutes in blood plasma pass from glomerular capillaries to glomerular capsule
– Glomerular filtrate - Filter 180 litres/day
- Eliminate 2 litres/day urine
- Glomerular capsule drains into renal tubule
Hormonal & Nervous Control of Renal Function
action of ADH
- Antidiuretic Hormone (ADH/Vasopressin) – Water Retention
- Increases aquaporin channels → More water reabsorbed → Urine concentrated.
- Low ADH → Water diuresis (dilute urine).
- Also acts as vasoconstrictor → Increases blood pressure.
Hormonal & Nervous Control of Renal Function
Renin-Angiotensin-Aldosterone System (RAAS
- Kidneys release renin → Triggers angiotensin II production.
Angiotensin II effects:
Vasoconstriction → Raises BP.
Stimulates aldosterone → Increases sodium & water retention.
- increasing blood pressure
Atrial Natriuretic Peptide (ANP)
- Released from stretched heart atria.
- Acts on kidneys to increase urine output → Lowers blood volume/BP.
- lowering blood pressure
Other mechanisms to control blood pressure in kidneys
- sympathetic nerves
- can decrease sodium and water excretion
- increase angiotensin 2 formation - parathyroid hormone
- increased reabsorption of calcium in DCT
the counter current multiplier
Descending Limb → Permeable to water, impermeable to salt → Water leaves, filtrate becomes concentrated.
Ascending Limb → Permeable to salt, impermeable to water → Salt pumped out, filtrate becomes dilute.
Creates a salt gradient in the medulla, allowing more water to be reabsorbed from the collecting duct when needed.
ADH regulates water reabsorption → More ADH = concentrated urine, Less ADH = dilute urine.
