Human Systems Phis Exam 3:(KIDNEYS)

What are the functions of the Kidney?

1. Remove waste products from the body

2. Maintain acid-base and water-salt balance

3. Regulate BP

4. Promote production of RBCs

5. Activate Vitamin D

MAINTAIN HOMESTATIS

What percent of cardiac output is done in the kidneys?

20%

What percent of ATP goes to the kidneys?

15%

How many times do you filter your entire plasma volume?

60 times a day

What are the processes of nephron?

1. Filtration

2. Reabsorption

3. Secretion

4. Excretion

STUDY ANATOMY

!!!!!

What is the path of blood through a nephron?

1. Artery

2. Afferent Arteriole

3. Golmerulus

4. Efferent Arteriole

5. Pertubular Capillaries

6. Vasa recta

7. veinV

Blood only filters what from plasma?

H2O, glucose, ions

What is the path of fluid (Filtrate) Through a nephron?

1. Blood

2. Bowman’s Capsule

3. Proximal Tubule

4. Descending limb of LH

5. Ascending limb of LH

6. Distal Tubule

7. Collecting Tubule

8. Collecting Duct

Processes of the Nephron: Filtration

From the glomerulus blood to the tubules, non-selective

Only size matters (coffee filter)

Processes of the Nephron: Reabsorption

Movement of solutes and water from lumen of tubules back into plasma

After filtration back to blood vessels. Is selective: requires channel from filtrate back into blood

Processes of the Nephron: Secretion

From Peritubular capillary blood to tubules, selective

Requires channel from blood into filtration

Processes of the Nephron: Excretion

From tubules to outside the body (urine)

The amount of substance X that is excreted in Joe’s urine increases. If the amount of the substance that was filtered did not change, what caused this increase?

If F is constant and E went up, either less of substance X was reabsorbed or more was secreted

Substance Y cannot be reabsorbed or secreted. If the amount of substance Y in the urine increases, what must have happened?

R and S are 0 so the only way to increase E is to increase F (E= F- R + S)

What are the three types of cells involved in Filtration?

1. Podocytes

2. Mesangial Cells

3. Endotheial cells

In Filtration: Podocytes

Wrap around glomerular capillaries, forming the filter through which plasma must pass.

In Filtration: Mesangial Cells

Support the glomerular capillaries and regulate blood flow through them

Filtrate must pass through what 3 layers?

Layers of Glomerular membrane

What are the layers of the glomerular membrane?

1. Capillary Endothelial cell

2. Basement membrane

3. Epithelial cell (podocyte)

Glomerular Filtration rate (GFR)

Amount of plasma filtered per unit time

GFR is determined by what?

Glomerular filtration pressure

Glomerular filtration pressure (GFP)

Driving force for filtration and is the sum of starling forces (pushing/pulling)

GFP Starling Forces

Pulling forces: Hydrostatic Pressure

Pushing Forces: Osmotic pressure

Under normal circumstances Pgc hydrostatic pressure created by BP is

The largest force contributing to GFP and thus GFR

If the efferent arteriole from the glomerulus is constricted, what happens to glomerular filtration pressure? Why? What happens to the glomerular filtration rate?

Constriction of the efferent arteriole will increase resistance and therefore increase GFP. Increased GFP will cause increased GFR

Steve’s blood albumin levels drop suddenly, what happens to GFR? Why?

Albumin is a large molecule that cannot cross capillary walls. It is a critical determinant of glomerular capillary osmotic pressure, which acts to reduce GFP. Reduced blood albumin would therefore reduce GFP, leading to increased GFP and GFR

Excretion is =

Filtration- Reabsorption + Secretion

Within the zone of auto-regulation: There are 3 mechanisms, of intrinsic control:

1. Myogenic Regulation

2. Tubulogomerular Feedback

3. Mesangial Cell Contraction

GFR is constant across a range of BP. How?

Zone of autoregulation: When GFR hit normal mean BP stays at that stop while increasing mean arterial BP

Kidneys keep BP regulated

Myogenic Regulation

Smooth muscle of the afferent arteriole contracts when it is stretched

Originating from muscle

Smooth muscle limits the amount of blood going in

Increased mean arterial pressure stretches the afferent arteriole, causing it to constrict

Tubuloglomerular Feedback

Macula densa cells release adenosine and ATP in response to increased flow

Tubules interacting with glomerulus

Cells sense changes in fluid flow

Mesangial Cell contraction

contract in response to stretching, decreasing the SA for Filtration

Decreases amount of filtration occuring

Explain the process of myogenic regulation in intrinsic control of GFR

1. Increase MAP

2. Increase Smooth muscle contraction

3. Increase resistance

4. Decrease blood flow

5. decrease Pgc

6. decrease GDP

7. Decrease GFR

Explain the processes of Tubuloglomerular Feedback in intrinsic control of GFR

1. Macula Densa cells sense increase in fluid flow by NACI

2. Secrete adenosin/ ATP

3. Increase contraction of smooth muscle

4. Increase resistance

5. Decrease blood flow

6. decrease Pgc

7. decrease GDP

8. Decrease GFR

Describe the process of Mesangial cells in intrinsic control of GFR

1. Increased mean arterial pressure in glomerular capillaries

2. Stretch of mesangial cells

3. Causes them to contract

4. Decreasing filtration surface area

5. GFR decreases

Outside the zone of auto-regulation, GFR is controlled extrinsically how?

1. TPR includes the kidney

2. Resistence in kidney capillaries

3. Sympathetic innervation

4. Decrease GFR

5. Decrease fluid loss

6. increase MAP

Extrinsic control of GFR

In response to an acute severe change in blood volume, GFR is reduced, conserving water

Baroreceptors detect decreased MAP and trigger renal sympathetic activity

Intrinsic control

Keeps GFR constance across a broad range of BP

Clinical implications of GFR

1. Filtered load

2. Clearance

3. Renal Plasma flow

Filtered Load

How much a particular solute is filtered per unit time.

FL= GFR x [x] plasma

Clearance

Volume of plasma cleared of a substance per unit time

Clearance= (concentration of x in urine) (Rate of urine production)/ concentration of X in plasma

Para- aminohippuric acid (PAH)

freely filtered, not reabsorbed. Any that is not filtered gets completely secreted

Inulin

Freely filtered and neither reabsorbed or secreted. clearance of inulin equals GFR

Creatinine

Occurs naturally in the body, freely filtered and only secreted in small amounts

Where does most reabsorption take place?

Proximal Tubules: Most

Distal Tubules: Fine tuning

In Reabsorption, what are the main barriers of movement?

1. Apical membranes

2. Basolateral Membranes

Of the tubular epithelium

What are the three types of reabsoprtion form filtrate back to blood?

1. Active solute transport

2. Passive water movement

3. Passive solute movement

In reabsorption: Active Solute Transport

Transporters can be on apical (x) or basolateral membrane (y)

Requires ATP and transporters

In reabsorption: Passive water movement

Transport of X and y increases plasma osmolarity so water follows (osmosis)

In reabsorption: Passive solute movement

Tubular concentration of solute Z is higher so it moved to the plasma (Often following water)

Down concentration gradient

What is the key for movement for solutes in the kidney?

Na+

Much of the energy used by the kidneys is for?

Na+/ K+ pump

What happens when the Kidneys capacity to reabsorb a substance is exceeded? GRAPH

The substance gets secreted because all transporters are used up (transport max)

Renal Threshold

Plasma concentration (glucose: example) when a substance is first detectible in urine

Diabetes Mellitus

Due to a deficiency in either secretion or response to insulin, glucose is not moved out of the blood and into cells

How do kidneys keep water?

1. Most of your body water comes in through food and drink

2. Most of your body water goes out in urine

3. Normally, fluid in = fluid out (Normovolemia)

What happens when fluid in does not equal fluid out?

1. Hypovolemia

2. Hypervolemia

Hypovolemia

(To little water in)

decreased plasma volume and results when water loss exceeds water gain

Hypervolemia

(Too much water in)

Increased plasma volume and results when water gain exceeds water loss

What are the consequences of hypovolemia and hypervolemia?

1. Changes in plasma volume directly affect MAP

2. Changes in plasma volume change osmolarity, affecting cells of the body

How do your kidneys change urine concetration?

By changing the permeability of the collecting duct

Increase aquaporins

concentrated urine

Reabsorb water

Decrease aquaporins

Diluted urine

excrete water

Kidney maintenance of fluid balance:

1. Diuresis

2. Antidiuresis

Diuresis

Excreting excess water (diluted urine)

Antidiuresis

conserving water, water back into plasma (Concentrated urine)

How is the kidney maintene fluid balance?

Changing permeability by altering number of aquaporins

How do your kidneys change urine concentration : Permeable membrane

Water flows out of the filtrate (concentrating the urine)

Antidiuresis

Response to hypovolemia

Lots of aquaporins

How do your kidneys change urine concentration: Impermeable membrane

dilute urine (diuresis

Response to hypervolemia

How do you change the number of aquaporins?

Circulating vasopressin binds to its receptor triggering a G-protein signaling cascade leading to the insertion of aquaporin 2 channels on the apical membrane,

How do you change the permeability of the collecting duct?

Regulating ADH

Low circulating ADH

Fewer aquaporins = reduced permeability= diuresis= dilute urine= removal of excess

High circulating ADH

more aquaporins= increased permeability= antidiuresis= concentrated urine= water saved

How is ADH regulated?

Posterior pituitary release ADH which up-regulates aquaporins, increasing urine concentration

Diabetes insipidus

Characterized by excessive urine and thirst.

Four types

1. Neurogenic

2. Nephrogenic

3. dispogenic

4. Gestational

diabetes insipidus: Neurogenic

Defect in the pituitary or hypothalmus- little production of ADH

Diabetes Insipidus: Nephrogenic

Defect in the kidneys’ response to ADH

Diabetes Insipidus: Dipsogenic

Damage to hypothalamic thirst center

Diabetes insipidus: Gestational

Overproduction of vasopressinase by mom

How does your body maintain Na+ homeostasis?

Regulating reabsorption

Na+ is freely filtered at the glomerulus and it is not secreted

How is Na+ reabsorbed?

1. Na+ / K+ pump moves Na+ out of cell into ECF

2. Na+ from tubular fluid moves down its concentration gradient into cell

How is Na+ reabsoprtion regulated?

By aldosterone

1. Increases the number of Na+ and K+ channels

2. Stimulates synthesis of Na+ and K+ pumps into basolateral membrane

More aldosterone =

More Na+ reabsorption and more K+ Secretion

How is aldosterone regulated?

1. Macula densa cells release adenosine in response to low Na+ in the distal tubule

2. This signal triggers granular cells to relase renin

Increased renin=

Increased aldosterone

The renin- angiotensin- Aldosterone System

1. Liver secretes angiotensiongen

2. Juxtaglomerular cells secrete renin which cleaves Angiotensignogen to Angionteniogen 1

3. Capillary endothelial cells secrete angiotension-converting enzyme which cleaves angiotensin 1 to angiotesin 2

4. Angiotensin 2 stimulates adrenal cortex to secrete aldosterone

Explain K+ homeostats

1. K+ is both reabsorbed and secreted in the nephron

2. K+ levels are regulated by secretion

3. Aldosterone has opposite effects on Na+ and K+

Increased aldosterone=

More Na+ reabsorption

More K+ secretion

Regarding Kidney Function

a. The clearaInce of glucose exceeds that of PAH

b. HCO3- is secreted

c. inulin is secreted

d. PAH is secreted

e. The clearance of inulin exceeds that of PAH

a. NO: plasma is completely cleared of PAH and glucose is reabsorbed

b. NO: Reabsorbed for bicarbonate

c. NO: Secreted or reabsorbed

d. YES

e. NO

Which one of the following statements about water reabsorption in the kidney is FALSE?

a. It takes place mainly in the proximal tubules

b. An increase in vasopressin will increase reabsorption

c. An increase in aldosterone will decrease water reabsorption

d. It depends on the proper functioning of the loops of Henle.

c. An increase in aldosterone will increase water absorption

Substances which are excreted at a higher rate than they are filtered include

a. inulin

b. glucose

c. PAH

d. Water

a. NO: Only filtered ( F=E)

b. NO: Filtered and reabsorbed (E=F-R)

c. YES: Excretion= Secretion + filtration (Completely cleared)

d. NO: filtered + reabsorbed (E= FML- R)

A person’s urine is tested and found to contain glucose. This person could have all the following except:

a. diabetes mellitus

b. Diabetes Insipidus

c. A filtered load of glucose greater than the Tmax for glucose reabsoprtion

d. A plasma glucose concentration greater than the renal threshold for glucose

B. Diluted urine