Digestion and Excretion Flashcards
What is digestion?
The process of breaking down food into molecules, small enough to be absorbed by the body
What is excretion?
The process by which metabolic wastes are eliminated
What are the two functions of the kidney?
Excretion
Maintenance of volume and composition of extracellular fluid
Describe the gross anatomy of the kidney
Renal capsule: Covers the surface of the kidney
Renal cortex: Outer layer of the kidney
Renal medulla: Inner layer of the kidney
Calyces (Major and minor): Cup-shaped funnels which collect the urine into the renal pelvis
Renal pelvis: Expanded area of the ureter that collects the waste products
Ureter: Tube which connects the kidney to the bladder
What are the basic functional units of the kidney called?
Nephron
What are the two main parts of the nephron?
Glomerulus
Tubular system
Where is the glomerulus located?
Renal cortex
What connects the kidneys to the bladder?
Ureters
What occurs during filtration?
Indiscriminate bulk flow from the blood (glomerulus) into the tubular system (Bowman’s capsule)
What causes the filtration in the bowman’s capsule?
Hydrostatic pressure in the glomerular capillaries > Hydrostatic pressure and protein osmotic pressure in the bowman’s capsule
Hydrostatic pressure in the glomerular capillaries favours filtration into the bowman’s capsule
How is the glomerulus adapted for filtration?
Capillaries are fenestrated
Endothelium of glomerular capillaries and epithelial layer of Bowman’s capsule connected to the basal lamina
What occurs during reabsorption?
Valuable substances are selectively reabsorbed from the tubular system back into the blood
Where does reabsorption occur in the nephron?
Proximal tubules
What occurs during secretion?
Further substances (waste metabolites) enter the tubular system
It requires active transport
Where does secretion occur in the nephron?
Distal tubules
What occurs in the head which aids with digestion?
Prehension (getting the food)
Mastication (chewing the food)
Salivation: Lubricating the food
Some species’ saliva contains amylase
What are the salivary glands and what do they secrete?
Partid: Serous
Mandibular: Mixture of mucous and serous
Sublingual: Mixture of mucous and serous
Buccal: Mixture of mucous and serous
Zygomatic: Mucous
Which salivary gland is only present in carnivores?
Zygomatic
What are the salivary conditions of the animals with simple stomachs?
Mainly mucous: To aid passage of food
Neutral pH: To allow action of amylase
What are the salivary conditions of the animals with complex stomachs?
Mainly serous: To provide optimum conditions for fermentation
Alkaline pH: To buffer forestomach for fermentation
How is salivary secretion regulated?
Sympathetic supply (fight or flight): Reduction
Vasocontriction
Parasympathetic supply (rest and digest): Increase
Vasodilation
What are the four types of motility in the digestive system?
Segmental contractions: To breakdown and mix food
Peristaltic contractions: To move food in a general aboral direction
Anti-peristaltic contractions: To move food in an oral direction
-To allow more time for digestion/absorption
-To allow rumination
-Vomiting
Mass movement: Extended peristaltic contraction used to empty sections of the GI tract
What is the role of mucus in digestion?
Lubricates food and protects mucosa
What pH is the stomach?
2
What pH is the small intestine?
6-7
What hydrolyse carbohydrates?
Amylase: Starch to disaccharides
Disaccharidases: Disaccharides to monosaccharides
What hydrolyse protein?
Pepsin
Trypsin
Peptidases
What hydrolyse fat?
Lipase
Phospholipase
(With the help of bile salts)
What is egestion?
Elimination of undigested food (pooing)
How is the proximal tubule adapted for its function?
Microvilli: Large surface area
Highly permeable to water/ions
How is the distal tubule adapted for its function?
Low numbers of microvilli
Low permeability
What are the three forms of reabsorption?
Primary active transport
Secondary active transport
Passive reabsorption
Describe primary active transport
Requires ATP
Sodium/Potassium pump on the basolateral membrane removes sodium ions and increases potassium ions in the cell
The sodium ions move into the cell from the tubular lumen down its concentration gradient
Describe secondary active transport
Sodium/Potassium pump on the basolateral membrane removes sodium ions and increases potassium ions in the cell
Symport: Substance (e.g. glucose) move into the cell against its concentration gradient, using the energy from the sodium ions moving down its concentration gradient
Antiport: Substance (e.g. hydrogen ions) is exchanged for the sodium ions
Describe passive reabsorption
Certain substances can move out of the tubular lumen into the epithelial cells down their concentration gradients/osmotic pressure gradient (diffusion/osmosis)
What is the difference between the descending and ascending limbs of the loop of Henle?
Descending:
Permeable to water
No ion pumps
Ascending:
Impermeable to water
Ion pumps which pump sodium, potassium and chloride ions out of the tubular lumen, increasing the osmolarity in the interstitial space
What is the function of the vasa recta?
They are arranged in a hairpin loop (like the loop of Henle) to maintain the concentration gradient around the loop of Henle
How does urine exit the body?
The urethral sphincter opens and the smooth muscle in the bladder wall contracts, forcing the urine through the urethra and out of the body
Which group of animals use fermentation to digest their food?
Vital in herbivores
Present to lesser extent in omnivores
Minimal in carnivores
Which animals are foregut fermenters?
Cows
Sheep
Which animals are hindgut fermenters?
Horses
Rabbits
What is the fermentation chamber in foregut fermenters?
Modified stomach
What is the fermentation chamber in hindgut fermenters?
Modified large intestine
Which animals don’t produce salivary amylase?
Dogs
Foregut fermentors
What are the four regions of a carnivores stomach?
Cardia
Fundus
Corpus
Pylorus
Why doesn’t the stomach walls get digested?
Epithelial cells produce bicarbonate rich mucous
What are the four types of cell in the stomach?
Mucous (goblet) cells: Secrete muscus
Parietal cells: Secrete HCl
Chief cells: Secrete pepsinogen
Entero-endocrine cells: Secrete hormones
What are the four chambers of a foregut fermenter stomach?
Abomasum (Simple stomach)
Omasum
Rumen
Reticulum
What are the four types of intestinal epithelial cell?
Goblet cells: Secrete mucous
Entero-endocrine cells: Release hormones and control digestive function
Paneth cells: Defence
Enterocytes (majority of cells): Absorption
Membrane bound enzymes
Describe the large intestine of carnivores
Short and simple
Similar diameter to the small intestine
Describe the large intestine of ruminants
Cecum present
Shorter than the small intestine but with a larger diameter
Describe the large intestine of horses
Well developed cecum and colon
What are the two cell types in the large intestine?
Colonocytes: Absorption
No villi, only crypts
Microvilli
Goblet cells (mainly in crypts): Secrete mucous
Why can’t mammalian enzymes digest cellulose?
They can’t break down the beta glycosidic linkages
What chemical acts as a buffer for the enzymes in the small intestine when food enters from the stomach?
Bicarbonate
What are the two transporter proteins which help absorb monosaccharides from the lumen into the bloodstream?
SGLT 1 (Sodium/Glucose co-transporter protein): From lumen into epithelial cell
GLUT2: From epithelial cell into the bloodstream
What is fermentation?
The breakdown of CHO by microbes in an anaerobic environment
The microbes break the beta glycosidic bonds
What are the end products of fermentation (waste products for the microbes but used by the host for energy)?
Volatile fatty acids:
Acetate
Butyrate
Propionate
What is the largest protein that can be absorbed without further breakdown?
Tripeptides (Three amino acids)
What is the difference between pepsin and pepsinogen?
Pepsinogen: Inactive enzyme which is released by chief cells
Pepsin: Pepsinogen which has been activated by the HCL (low pH) in the stomach lumen
What are triglycerides (fats) made of?
A glycerol backbone joined to three fatty acids
How are fats absorbed?
The bile salts create small fat droplets micelles which can merge with the cell membrane
Describe swallowing
Upper oesophageal sphincter relaxes
Peristaltic wave carries food/fluid into the stomach
Describe the motility in the cows stomach
Primary contraction: Mixing food
Secondary contraction: Movement of gas out of the stomach
Rumination contraction: Anti-peristaltic (chewing the cud)
Describe the motility in the horses large intestine
Caecum: Mixing and mass movement
Ascending colon: Segmental, anti-peristaltic and peristaltic waves
Descending colon: Segmental and peristaltic
