11.1 overview and kidney structure

osmosis

passive transport of water across a selectively permeable membrane in response to solute concentration gradients, pressure gradients, or both

solute concentration is measured as __ in

osmolarity, milliosmoles per liter of solution (mOsm/L)

water moves osmotically from a solution of __ osmolarity to one of __ osmolarity aka from where there is __ “free'“ water to where there is __

lower, higher, more, less

osmoregulation

maintaining osmolarity of body fluids

+which way will water go?

B, to the right

osmotic pressure

the minimum pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane

purpose of osmoregulation in animals

to keep osmosis from shrinking or swelling their cells — want to keep cellular and extracellular fluids isoosmotic

osmoregulators

keep the osmolarity of body fluids different from that of the env

osmoconformers

allow the osmolarity of their body fluids to match that of the env

excretion is coupled with osmoregulation how?

• molecules and ions are removed from the body to keep cellular and extracellular fluids isoosmotic

• in most animals, extracellular fluids are filtered through tubules formed from transport epithelium (layer of cells w transport proteins in their membrane) and released to the exterior of the animal as urine

1.

filtration: small molecules and ions from body fluids or blood NONSELECTIVELY pass through narrow spaces between cells into the tubule

2.

reabsorption: nutrient molecules, some ions, and conserved water are returned to the body fluids or blood by transport epithelium

3.

secretion: excess ions and toxic breakdown products are transported SELECTIVELY from the body fluids or blood into the tubule

4.

release: urine (nitrogenous wastes, some ions, toxic breakdown products, excreted water) is released into the environment

what gets reabsorbed generally? where does this occur mostly in the kidney?

glucose, amino acids, ions: Na+, K+, Cl-, water, HCO3-

in kidney, this occurs mostly in the proximal convoluted tubule

what gets secreted, why, and where?

H+, K+

important for maintaining ion and pH balance

in the kidney, occurs mostly in the distal convoluted tubule

what gets excreted?

substances that are unneeded or are in excess: wastes such as nitrogen compounds, NH3 (ammonia)

secretion

• the discharge of wastes from the body fluid into the filtrate

• selective process in which specific small molecs and ions are transported from the blood into the excretory tubules

excretion

• elimination of substances from the body

• disposal of nitrogen containing waste products of metabolism

ammonia + who excretes

toxic, must be diluted to be excreted, usually aquatic animals excrete this

urea + who excretes

made from combining ammonia w HCO3-, requires less water than ammonia, mammals, most amphibians, sharks, some bony fishes

uric acid + who excretes this

conserves even more water, birds, insects, many reptiles, land snails

renal artery

from the abdominal aorta, supplies kidney w blood

renal vein

goes to the inferior vena cava

heart, diaphragm, adrenal gland, right kidney, left kidney, inferior vena cava, abdominal aorta, ureter, urinary bladder, urethra

in mammals, urine is __ to body fluids bc it conserves __. almost all other vertebrates produce urine that is __ to body fluids

hyperosmotic, water, hypoosmotic

production of hyperosmotic urine (more concentrated) is accomplished by specialized structures in the

kidney

kidney structures (__) have __ (established by specific __ in specific regions)

nephrons, permeability differences, transport proteins

different __ of molecules and ions in the __ in the __

concentration gradients, interstitial fluid, kidney

__ surrounding the nephron reabsorb ions, water, and other molecules that have been secreted into the nephron

network of capillaries

renal medulla, renal cortex, renal artery, renal vein, renal pelvis, ureter

bladder wall, ureter, sphincter muscles, body wall, urethra, opening to exterior

juxtamedullary neuron, cortical nephron, renal cortex, renal medulla

nephron, bowman’s capsule, renal cortex, renal medulla, descending segment of loop of Henle, ascending segment of loop of Henle, collecting duct

urine production - overview

• leaves individual nephrons

• is processed further in collecting ducts

• pools in the renal pelvis

• flows through the ureter to the urinary bladder

• flows through the urethra to the exterior of the animal

blood flow in the kidney - overview

• blood flows into the kidneys through the renal artery, to interlobular artery, to afferent arteriole, and enters the glomerulus (cluster of blood vessels) in Bowman’s capsule (cup-like part of the nephron that is around the glomerulus)

• in the glomerulus, the blood flow is split into 50 capillaries that have very thin walls

• the solutes in the blood are easily filtered thru spaces in these walls due to the pressure gradient that exists btwn the blood in the capillaries and the fluid in the Bowman’s capsule

• the pressure gradient is controlled by the contraction or dilation of the arterioles

• after passing through the efferent arteriole, the filtered blood enters the vasa recta blood vessels near the Loop of Henle

proximal convoluted tubule, efferent arteriole, afferent arteriole, artery (branch of renal artery), cortex, medulla, vein (drains ultimately into renal vein), descending segment of loop of Henle, peritubular capillaries (vasa recta), ascending segment of loop of Henle, glomerulus, Bowman’s capsule, distal convoluted tubule, collecting duct, to renal pelvis

nephron

• a structure in the kidney; specialized tubule involved in osmoregulation/excretion

• each human kidney has > 1 million nephrons

• juxtamedullary nephrons: 20%, long loops that extend into the medulla

• cortical nephrons: 80%, short loops mostly located in the cortex

vasa recta

• blood vessels around the loop of Henle in medulla region (note: peritubular capillaries are located more cortically)

• are important in maintaining the ion gradient of the medulla to facilitate osmosis with the loop of Henle