Biochemistry Class 9 - Renal and Digestive Systems

What are the excretory organs (3)?

Colon, liver, kidney

What does the colon do?

Excretes material that was eaten, but not absorbed

Solid waste

What does the liver do?

Excretes material that was eaten and absorbed, but not dissolved in plasma

Eliminates hydrophobic waste

What does the kidney do?

Eliminates material that was eaten, absorbed, and dissolved in the plasma

Hydrophilic waste

Regulates blood pressure, ion balance, water balance, pH

Secretes erythropoietin to stimulate red blood cell formation

Activates vitmain D

Why are kidneys sensitive to drops in oxygen?

Its functions involve a lot of active transport → thus ATP → thus oxygen

When O₂ drops → send out erythropoietin → make more RBCs to carry more O₂

What is the anatomy of the renal system?

Kidneys, ureter, bladder, urethra, internal urinary sphincter, external urinary sphincter

All but kidneys are muscular → push urine through

What does the internal urinary sphincter do?

Smooth muscle, involuntary control of urination

What does the external urinary sphincter do?

Skeletal, voluntary muscle

Voluntary control of urination

Below internal urinary sphincter

What is the anatomy of the kidney?

Renal pelvis, ureter, cortex, medulla, nephron

What is a nephron?

Functional unit of the kidney

How does urine go through kidneys?

Nephron begins in cortex → can dip into medulla → filters blood → blood travels through it → drains into renal pelvis → cannot be modified → into ureter

What three processes do nephrons do?

Filtration: moves blood plasma across the capillary wall (single layer of cells) using blood pressure → why kidneys regulate blood pressure

Reabsorption: move a substance from the filtrate back to the blood (glucose, amino acids, water)

Secretion: move a substance from blood and into filtrate (drugs, toxins, creatinine)

Ions are reabsorbed (Na⁺, HCO₃^-) and secreted (H⁺, K⁺) as necessary

How long can you live without functional kidneys (with no intervention)?

2 days

What is the glomerular filtration rate (GFR)?

125 mL/min

How much blood kidneys filter

Entire blood volume in under an hour

What is the structure of the nephron?

Capsule: glomerulus

Tubule: proximal convoluted tubule, loop of Henle, distal convoluted tubule

Collecting duct

Why are glomeruli important? Why are they unique?

Filter blood: they are porous enough to let small molecules through, but not proteins or cells

Special: supplied with blood an artery and drained by an artery (not a vein)

How does the glomerulus recieve and get rid of blood?

Receives through afferent arteriole (approaching)

Gets rid of through efferent arteriole (exit)

Important that both are arteries → they can contract to help control pressure → blood filters at a normal rate

What is the proximal convoluted tubule?

Twisted up part of tubule closest to glomerulus

Most reabsorption and secretion

Relatively unregulated

What does the loop of Henle do?

Sets up a gradient in the medulla (saltiness/osmolarity increases as you get further into the medulla)

Each side of the loop has different permeabilities: descending side is only permeable to water, ascending side is permeable to salt and not water (active transport at the top)

No gradient in descending side, but a gradient is set up in the ascending side

Blood in efferent arteriole (does not have much water/super concentrated with proteins and shit) passes by the loop of Henle → water drawn in → this removes the water and sets up a salt gradient in the medulla

How concentrated is urine once it passes through the loop of Henle?

4x more concentrated than normal plasma for short loops

Some animals have lots of long loops, so up to 12x more

In humans, after the loop of Henle, urine is roughly isotonic to plasma

What does the distal convoluted tubule do?

DCT

Specialized reabsorption and secretion

Where aldosterone, parathyroid hormone, and calcitonin affect sodium and calcium reabsorption

What does the collecting duct do?

Picks up urine from several nephrons

Regulated water reabsorption → retain more if dehydrated

Based on ADH (antidiuretic hormone)

ADH increases how much water is retained by increasing the permeability of the cells to water

How do diuretics work?

Inhibit ADH so you do not retain water when your body needs it

What is the renin-angiotensin system?

Blood pressure falls → kidney secretes renin → angiotensinogen converted to angiotensin I → active → angiotensin converting enzyme (ACE) converts angiotensin I to II → systemic vasoconstriction and increased aldosterone release

How does systemic vasoconstriction affect blood pressure?

All arteries are contracted → increases blood pressure

How does increased aldosterone release affect blood pressure?

Aldosterone released → increased Na ⁺ reabsorption → increases blood osmolarity → increased release of ADH → retain more water → increased blood volume → increased blood pressure

Why is blood pressure important?

If too low → cannot drive the flow of blood (organs do not get enough blood)

If kidneys do not get blood → no filtration

What is the juxtaglomerular apparatus?

Contact point between afferent artery and distal convoluted tube (because they are all twisted and shit)

Afferent artery has baroreceptors → detect fall of blood pressure → release renin

Distal tubules have chemoreceptors → detect filtrate osmolarity falling → stimulate afferent artery to release renin and directly dilates the afferent artery

How does ANP regulate blood pressure?

High blood pressure → atria of heart stretch → right atrium releases ANP (atrial natriuretic peptide) → vasodilation and inhibition of renin and aldosterone release

Prevents retention of sodium, thus water

How is pH regulated by the kidney?

Takes several hours/days → respiratory can do this in a couple seconds

All kidney tubule cells have lots of carbonic anhydrase → always have H⁺ and HCO₃^-

Generally reabsorb bicarbonate and secrete protons

Blood pH is 74, urine pH is 6.5

When blood pH is too high, stop absorbing bicarbonate

Stop secreting hydrogen when blood pH is high

When pH is low: absorb more bicarbonate, secrete more protons

What are the digestive accessory organs?

Digestive role, but not part of digestive tube

Liver, gallbladder, pancreas, salivary glands

What does the liver do for the digestive system? Is it essential?

Produces bile

Cannot live without it

What does bile do?

Emulsifies fat for easier digestion

Fat wants to clump in fat globs → hard to digest → bile is amphipathic and breaks big fat globs into small ones → easier to digest

Does not actually digest anything

What does the gallbladder do? Is it essential?

Stores and concentrates bile

You can live without it, but cannot eat very high fat diets

What causes gallstones?

Gallbladder stores and concentrates bile too well → bile mixes with cholesterol and such → jam bile duct → gallbladder inflames → impaired

What does the pancreas do? Endocrine role

Excretes insulin and glucagon

What does the pancreas do? Exocrine role.

What if it cannot do this?

Source of digestive enzymes: proteases, lipases, amylases, nucleases

Produces bicarbonate to neutralize stomach acid and bring intestinal pH to a more normal level (6 -7)

If your pancreas is non-functional → malnutrition

How is the alimentary canal wall structured?

From inner to outer: lumen → mucosa → submucosa → circular muscle (runs around) → longitudinal muscle (runs parallel) → serosa (connective tissue)

How do circular and longitudinal muscles function in digestion?

Circular muscles constrict → where they are super thick and contract enough to close the tube, they are called sphincters → act as valves

Longitudinal muscles cause the tube to become shorter → helps with peristalsis

What is peristalsis? Analogy.

Movement through digestive tract

Like threading a drawstring through a sweatpants band

What is the function of the mouth?

Grind food, moisten food, begin starch digestion

What is the structure of the mouth?

Teeth, tongue, salivary glands (technically a digestive accessory organ)

What is the exocrine function of the mouth?

Saliva: mostly water, mucus, and enzymes

Slightly basic

Lysozyme kills bacteria

Amylase digests starch

What are endocrine functions of the mouth?

None

What is the function of the esophagus?

Tube to bring food to stomach

What is the structure of the esophagus?

Stars as skeletal muscle (voluntary) → becomes smooth (involuntary)

Cardiac sphincter: prevents stomach contents from refluxing → failure causes acid reflux

What are exocrine secretions of the esophagus?

Mucus

What are endocrine secretions of the esophagus?

None

What is the function of the stomach?

Very limited digestion and absorption

Storage tank for food

What is the structure of the stomach?

Gastric glands

Pyloric sphincter: regulates entry into small intestine

What is the anatomy of gastric glands?

Mucus cells at top of pit

Parietal cells midway down

Chief cells at the bottom

What are exocrine secretions of the stomach?

Mucus cells make mucus

Parietal cells secrete HCl

Chief cells secrete pepsinogen (innate immunity) (inactive form is secreted → travels to lumen → activated by acid)

What does pepsinogen do?

Degrades proteins of bacteria, viruses, and some neurotoxins

What is the endocrine function of the stomach?

G cells scattered throughout the stomach lumen secrete gastrin

What does gastrin do? How is it regulated?

Hormone that increases activity of gastric glands → decreases pH

Regulated via negative feedback of pH: pH falls → release of gastrin stops → gastric glands stop → pH rises)

What is the function of the small intestine?

Almost all digestion and absorption

What is the structure of the small intestine?

Duodenum: first ~5%

Jejunum: mid ~40%

Ileum: last ~55%

Massive increase in surface area for absorption

What causes the increase in surface area in the small intestine?

Mucosa folds up (folds called plicae)

Plicae have villi

Villi have microvilli

All serve to increase surface area

What are exocrine secretions of the small intestine?

Enterokinase (aka enteropeptidase)

Brush border enzymes

What does enterokinase do?

Activates trypsinogen to trypsin (pancreatic protease) to set of a cascade of enzyme activations

What are inactivated enzymes called?

Zymogens

Named “(name of enzyme) ogen”

What do brush border enzymes do?

Disaccharidases and dipeptidases

Last step in digestion of sugars and proteins

What are endocrine secretions of the small intestine?

Enterogastrone

CCK (cholecystokinin)

Secretin

What is enterogastrone?

Hormone of small intestine

Reduces stomach motility triggered by food in the intestine → so you do not put too much in at once

What does CCK (cholecystokinin) do?

Hormone of small intestine

Increases bile release from liver and gallbladder

Triggered by fat and proteins

What does secretin do?

Hormone of small intestine

Increases bicarbonate release from pancreas

Triggered by low pH

What is the function of the large intestine?

Reabsorb water

Stores feces

What is the structure of the large intestine?

Colonic bacteria

Ileocecal valve

Internal/external anal sphincters

What do colonic bacteria do?

Secrete vitamin K

Digest leftover nutrients so pathogenic bacteria cannot grow

What is the role of the ileocecal valve?

Usually closed

Relaxes when there is food in stomach → you have to shit 30 mins after eating ish

What are the internal and external sphincters?

Internal: smooth/involuntary

External: skeletal/voluntary

Allow you to shit (like urinary sphincters do for peeing)

What are the exocrine secretions of the large intestine?

None

What are the endocrine secretions of the large intestine?

None