Maintain's homeostasis by regulating volume and composition of the blood. Elimination of waste products must be excreted in solution. And, the kidney must be capable of producing a concentrated filtrare (in order to maintain water). This is made possible by:

-filtration: blood pressure forces water across a filtration membrane

-reabsorption: removal of water and solutes forom the filtrater across the tubular epithelium and into the tubular fluid.  involves simple diffusion or active transport

-

-secretion: transport of solutes from peritubular fluid across epithelium and into tubular fluid.  This is necessart, because filtration does not force ALL dissolved materials out of the plasma.

-branching network of capillaries; blood flows into the glomerular capillaries through the afferent arteriole.

-endothelium is fenestrated, which allows large amounts of solute-rich, protein-free fluid to pass from the blood into Bowman's capsule. Once this plasma-derived fluid is within Bowman's capsule is called filtrate.

What is the bowman's capsule and what does it do?

-outer layer is called parietal layer formed by flattened epithelium:

-inner layer called visceral layer lines capillaries and coninuous with the outher later, formed by podocytes

-has afferent (arrives) and efferent (exits) arteriole

-unusal cells with cellular extensions called foot processes which come in contact with the capillaries of the glomerulus; they form filtration slilts that allow fluid and small molecules to exit the blood; but do not allow the filtration of blood cells or large protein molecules form blood.  

-the arterioles are high resistance blood vessels, the diameter of afferent is greater than the diameter of the efferent

-The high resistance of the afferent arteriole protects the glomeruli from large fluctuations in the systemic BP.

-resistance in the efferent arteriole reinforces the high glomerular BP and reduces hydrostatic pressure in the peritubular capillaries and vasta recta.

-arise from the efferent arterioles draining the capillaries of the glomeruli of cortical nephrons

-run alongside renal tubules within the renal cortex and empty into the venules of the renal venous system

-low pressure, porous capillaries that readily take up solutes and water from the tubule cells as these substances are reclaimed from the filtrate

-juxtamedullary nephrons, efferent arterioles give rise to bundles of long straight vessels that run beside the loops of Henle deep into the medulla.

-occurs only within the renal corpuscle

-fluid moves across the wall of the capillaries and into the capsular space

-this fluid encounter three barriers:

1. capillary endothelium of the glomerulus (fenestrated)

2.fused basement membranes of the capillary endo. and basement membrane of the podocytes

3. filtration slits formed by the foot processes of the podocytes, make blood cells and most large protein molecules in plasma incapable of filtration.

Glomerular Filtration:

Filtrate vs. urine

-starts containing everything that blood plasma has besides proteins then when it reaches the end of the nephron it has lost most of its water, nutrients, and essential ions, which is not urines and contains metabolic wastes.

-kidney's produce 180 liters of filtrate per day and only 1.5 (1%) is excreted as urine

-glomerular filtration: because the fenestrated endothelium is 1000x more permeable than ordinary continous capillaries and glomerular hydrostatic pressure is much higher than that of other capillary beds. This results in a substantial positive net filtration pressure.

-the total amount of filtrate formed per minute by the kidneys.

-influenced by:

1. total surface area

2. Filtration membrane permeability

3. net filtration pressure.

Normal GFR in both kidneys in adults is 120-125 mL/min

-an increase in arterial blood pressure will increase GFR, while dehydration will decrease GFR.

-VERY important to maintain this plays a role in how much water and solutes are reabsorbed.

-when its fast substances are lost in urine, when its slow wastes are reabsorbed.

Renal Auto-regulation, Hormonal Regulation, and Neural Control.

-Refers to kidney's intrinsic ability to adjust its own resistance to blood flow. The goal of this is to maintain an adequate GFR despite changes in local blood pressure and blood flow.

-accomplished by changing diametes of arterioles in glomerus

-myogenic muscle mechanism that responds to changes

-increase in BP cause afferent to constrict which restricts blood flow into glomerulus

-decrease in BP cause afferent to dilate as to increase the glomerulus and offset any decrease in glomerular pressure due to decrease in BP

-each nephron has a region called jux. apparatus where the intial portion of the DCT lies against the afferent arteriole

-inside the arteriole walls are juxtaglomerular cells, which contain large amounts of secretory granules containing renin. they act as a mechanoreceptors to directly sense the blood pressure in the afferent arteriole.  If the BP is too low, renin will be released.

-mancula densa measure the sodium concentration of the filtrate and use this as a judge as to whether BP or blood volume are ar homeostatic levels.

-Renin increases BP and Atrial Natriuretic Peptide (ANP) increase GFR and decrease blood volume and pressure

-produced by JC cells of jux. apparatus

-converts inactive angiotensin I into the active angiotensin II which is a strong vasoconstrictor; renin also stimulates the activity of ADH and aldosterone.

-it is released when renal blood flow declines due to decrease in blood volume; there is a fall in systemic pressure or blockage in the renal circulation causing a decrease in GFR.

-overall effects are an increase in BP in systemic blood pressue and blood volume and therefore the restortation of a normal GFR

Atrial Natriuretic Peptide

(ANP)

-released in response to the stretching of the atrial walls of the heart by increase blood volume or BP.  Along with other affects:

-causes the dilation of the afferent arteriole and constriction of efferent arteriole with the effect of increasing GFR and decrease blood volume and pressure.

-sympatheric nervous system response when mean blood pressure is drastically lowered.

-afferent arteriole vasoconstriction lower blood flow and therefore the GFR to maintain blood volume and blood flow to the essential organs of the body (brain, heart, and skeletal muscle.)

-filtration of plasma which genereates about 180 liters a day of filtrate which is similar to blood plasma but without the proteins

-it uses net filtration across a filtration membrane

Tubular Reabsorption

-filtrate first passes into interstital spaces of the kidney, and then into the peritubular capillaries which are in close promx. to the tubules.

-movement of fluid out of the tubules can occur through either passive (diffusion and/or osmosis) or active transport processes, depending upon the region of the nephron.

-fluid within the capsular space and the nephron tubules

-fluid within the interstitial spaces of the kidney or fluids surrounding the nephron tubules

-first place it is found is in the minor calyx

-it is the final product once fluid has flowed through the whole nephron

-movement of substances from the tubular fluid into peritubular; bringing substances back into the body

-movement of substances from the tubular fluid to the tubular cells into from cells to fluid, removing substances from the body into filtrate.

1. Diffusion

2. Facilitated Diffusion

3. Osmosis

4.Co-Transport

5. Counter-Transport

-substrate that binds to a carrier protein  that facilitates movement across a membrane

-Given carrier protein works in only one direction (depends upon gradients and location of proteins)

-distributions of proteins can vary from one cell surface to another

-membrane of a single tubular cell contains many diff. tpyes of car. pro.

-Carrier proteins can reach a saturation point, some of the material will remain in the tubular fluid and appear in the urine. (ex. glucouse in the blood enters nephron filtrate, however all is reabsorbed. In humans strictly controlled around 100mg/100ml of plasma, max is 400 over 100)

-osmosis is the only way reabsorption of water can occur. Always passive and will always diffuse from low to high osmotic pressures

How much of isotonic concentration of slats or electrolytes in plasma or other fluids?

Some of the major steps in production of concentration of urine.

-300 m0s11

-same salt osmolarity/ concentration as plasma

-the capsular space is blind-ended and connected to PCT, all filtrate is brought into nephron tubules.