portage learning biol 252 module 7 urinary system

herba sherba

Functions urinary system

Cleansing body of wastes to produce urine, regulating pH, and assist with blood pressure.

incontinence

loss of control over urination due to nervous system failure.

nephrons

functional unit in the kidney

what do nephrons do

filter and make ur ine

How many nephrons in a kidney

1 million

2 types of nephrons

juxtamedullary nephrons, cortical nephrons

juxtamedullary nephrons

have longer loops that extend into the renal medulla

cortical nephrons

have loops that stay in the cortex

filtrate

(blood plasma minus the proteins) of the blood and modify it into urine, which is then excreted out of the body

2 structural components of a nephron

the renal corpuscle and the renal tubule

renal corpuscle

made of the glomerular capillaries and the glomerular capsule. Filters blood to form filtrate

glomerulus

cluster of fenestrated capillaries with a special filtration membrane

renal tubule

which is made of the proximal and distal convoluted tubules and the the nephron loop. Reabsorption and secretion → urine formation

renal corpuscle

consists of a tuft of capillaries called the glomerulus

Bowman’s (glomerular) capsule.

cup-shaped structure that surrounds the glomerulus in the nephron

Fenestrated endothelium

innermost layer of the filtration membrane and consists of endothelial cells

fenestrations

small pores. allow small molecules like water, ions, and small solutes to pass through, facilitating filtration from the blood into the renal capsule.

basement membrane

composed of glycoproteins and collagen fibers. The basement membrane acts as a physical barrier, preventing larger proteins and blood cells from passing through into the filtrate.

Charge of basement membrane

negative.

Podocytes

uniquely shaped cells with extending finger-like arms called pedicels that tightly cover the glomerular capillaries. These projections interdigitate to form filtration slits, leaving very small gaps between the digits to form a sieve.

3 layers of flitration membrane

Fenestrated endothelium, basement membrane, Podocytes

juxtaglomerular apparatus (JGA)

specialized regulatory structure of the nephron that controls blood pressure, blood volume, and glomerular filtration rate (GFR).

macula densa

forms a part of the JGA. Releases ADP and adenosine. Monitors flow of filtration.

juxtaglomerular cells (JG)

These cells play a critical role in blood pressure regulation and filtration of the kidneys. modified smooth muscle cells lining the afferent arteriole and renin release

mesangial cells

in the JGA that can contract and relax to help regulate the rate of filtration of the glomerulus. 

brush border

Simple cuboidal cells form this tubule with prominent microvilli. these microvilli create a large surface area to maximize the absorption as 65% of the filtrate volume is reabsorbed by the PCT

Secondary active transport

process by which the energy stored in the electrochemical gradient of one molecule is used to drive the transport of another molecule against its own gradient. 

loop of Henle (nephron loop)

helps to reabsorb water and salt from the kidney tubules. associated with the "thick" segment made from cuboidal to columnar epithelium and reabsorbs sodium, potassium, and chloride ions

collecting ducts

lined with simple cuboidal cells. The collecting duct marks the end of the nephron. It is the final site of water reabsorption, regulated by antidiuretic hormone (ADH), which concentrates urine.

What are collecting duct lined with

lined with simple cuboidal cells (principal cells) or ciliated columnar epithelium (intercalated cells)

aquaporin-2

These channels allow for water to pass through the cells and back into the blood

papillary duct,

empties into a minor calyx. The papillary duct contains columnar cells.

Urine formation

2 L of 180 filtrate is urine. 25 % of bodys energy. 20% of body blood enters kidneys.

Filtration

Happens in glomerulus, water small solutes forced out of blood. Then goes into bowmans capsule.

Tubular fluid

fluid in PCT

Reabsorption.

takes place along the entire tubule portion. Water, glucose, amino acids, and other necessary ions are reabsorbed back into the blood capillaries that closely follow the nephron. 

Tubular secretion

Toxins, waste products, hydrogen ions, and potassium ions are actively secreted and removed

glomerular filtration rate

The volume of filtrate that enters the glomerular capsules formed by both kidneys per minute is termed the glomerular filtration rate

GFR

The average GFR is 125 mL/min. Typically, an increase in the GFR will mean an increase in the volume of urine produced, and a decrease in the GFR will mean a decrease in the amount of urine produced.

Hydrostatic pressure

pressure produced by a fluid against a surface

Glomerular hydrostatic pressure (GHP)

the pressure that the blood exerts on the glomerular capillaries. This pressure tends to push water and solutes out of the blood and into the capsule. GHP tends to be around 50 mmHg,

Capsular hydrostatic pressure (CsHP)

opposes GHP and tends to push water and solutes out of the filtrate and back into the glomerular capillaries. around 15 mmHg

net hydrostatic pressure (NHP)

The difference between GHP and CsHP is called the net hydrostatic pressure (NHP)

Osmosis

movement of solvent (water) across a membrane that is impermeable to a solute in the solution

osmotic pressure

solute concentration is the same on both sides of a semipermeable membrane

Osomosis higher in bowman or glomerual capillary?

osmotic pressure inside the glomerular capillary is higher than the osmotic pressure in Bowman’s capsule

blood colloid osmotic pressure (BCOP)

25 mmHg, which tends to draw water out of the filtrate and back into the plasma.

Bowman’s space

absence of proteins in Bowman’s space (the lumen within Bowman’s capsule) results in an osmotic pressure near zero.

systemic edema

Less osmotic pressure pulling water into the capillaries tips the balance towards hydrostatic pressure, which tends to push it out of the capillaries. This “plumps up” the tissues and cells

Factors that determine GFR

-The total surface area: Larger SA allows for efficient filtration.

-permeability of the filtration membrane: A membrane with higher permeability facilitates greater passage of substances, thereby, enhancing filtration.

-The net filtration pressure (NFP) which represents the balance of forces favoring and opposing filtration across the glomerular capillaries, influences GFR.

NFP

NFP = Glomerular hydrostatic pressure (GHP) – [capsular hydrostatic pressure (CHP) + blood colloid osmotic pressure (BCOP)] = 10 mmHg

That is:

NFP = GHP – [CHP + BCOP] = 10 mmHg

shock

Extremely low blood pressure can lead to shock, which is life-threatening.

Intrinsic controls

involve mechanisms inherent within the kidneys themselves, including the autoregulation of renal blood flow

Extrinsic controls

involve neural and hormonal regulation originating outside the kidneys

arteriole myogenic mechanism

When stretched, it contracts, when stretching stops, it relaxes. Allows for vasoconstriction and vasodilation.

Explain how arteriole myogenic mechanism works with high BP

Smooth muscle stretches due to high bp, causes the muscles cells to contract because the mechanism contracts when it stretches, it causes vasoconstriction, and decreases flow.

tubuloglomerular feedback

Cells of JGA. The cells in the macula densa which are at the end near the distal convulated tubule detect solute conentration inside teh DCT, and release signals to the afferent arteriole.

High blood pressure and Tubuloglomerular feedback?

High blood pressure, meaning GFR tends to increase

• Filtrate moves quickly through tubule which is bad

• There is an increased concentration present in the macula densa due to high BP, and the tubuloglomerular feedback senses that.

• It releases signals like ATP and adenosine to cause vasoconstriction

• Resistance increaes, reducing blood flow, and brining back glomural filtration rate.

Sympathetic nerves:

kidneys are innervated by the sympathetic neurons of the autonomic nervous system

epinephrine

Stimulation of the sympathetic nerves also causes stimulation of the adrenal medulla, which, in turn, produces a generalized vasoconstriction through the release of the hormone epinephrine

Epinephrine

acts to vasoconstrict the afferent arterioles, further reducing the volume of blood flowing through the kidneys

Purpose of epinephrine in survival situation?

This process helps redirect blood to other organs with more immediate needs for threat survival.

RAAS

Regulates BP

Fluid balance

Vascular resistance

RAAS system and how it works

IF there is low blood volume or pressure or osmolarity then:

• Kidneys release renin

• Renin then triggers angiotensinogen to angiotensin 1

• Angiotensin 1 then is converted to angiotensin 2 via ACE

Functions of angiotensin 2

Starts vasoconstriction, increases BP

Functions of angiotensin 2 in terms of kidneys

Stimulates the tubules, to reabsorb Na+ and water, and increaes blood volume and BP.

Aldosterone/Angiotensin 2

Adrenal cortex is stimulated to secrete aldosterone, which is a salt retaining hormone.

Increases blood volume and BP.

Angiotensin 2 and ADH

ADH is secreted as well by the posterior pituatary, and it retains water to increase blood volume, and then BP

Angiotensin 2 and thirst center

Stimulates thirst center in hypothalamus,

increases blood volume, and BP.

What does ANP (atrial natriuretic peptides) do?

Stop sodium recovery, causing water loss (increased urine formation), which lowers blood volume, and BP.

Diuretics

Drugs that increase water loss, and can lower BP.

ADH

Opposite of diuretic, it promotes recovery of water, decreasing urine output, increasing blood volume, and BP.

inulin

Used to determine GFR. Can’t be reabsorbed or secreted.

estimated GFR (eGFR)

calculated by creatinine and/or cystatin C.

• used to assess kidney function by estimating the rate at which the kidneys filter blood.

Creatinine

produced by muscle metabolism and is excreted by the kidneys and not reabsorbed by the nephron.  Elevated levels of serum creatinine indicate impaired kidney function.

Cystatin C

protein produced at a constant rate by cells throughout the body and is filtered by the glomerulus, keeping it in proper ranges. If kidney function deteriorates, cystatin C levels will increase.

blood urea nitrogen (BUN)

blood test that measures the amount of nitrogen in the form of urea in the bloodstream. High BUN level can indicated deficient filtration of kidneys. Low BUN means overhydration.

tubular fluid

Once the filtrate enters the renal tubules, it is called tubular fluid

Reabsorption

second step in urine formation, involves the recovery of water and solutes from the tubular fluid, returning them to the blood.

secretion

process where waste products, unneeded solutes, and toxins are added to the tubular fluid for eventual excretion as urine

Simple diffusion

Substance moves down concentration gradient higher to lower.

Osmosis

Diffusion of water from higher potential to lower potential.

What allows for osmosis

Aquaporin.

Fascilitated diffusion

Same as simple diffusion however, a channel or protein carrier is required. Good for lipids, and larger substances.

Active transport

Substances moved against concentration gradient from lower to higher. Requires ATP. Na+ K+ pump.

Secondary active transport

Indirect usage of energy for facilitated diffusion. Energy that is already present in the gradient is used.

Sodium Glucose Transport (SGLT)

• Na/K Pump

• Uses the Na Concentration gradient

• Na flows into the cell

Cotransport (symport

mechanisms move two or more substances in the same direction at the same time

countertransport (antiport

mechanisms move two or more substances in opposite directions across the cell membrane.

Specificity

binding is specific; a specific substrate must bind to its specific carrier protein.

Cell surfaces

The type of carrier proteins can vary on the cell surfaces. For transport to occur, the material must enter a cell at the one surface and then leave the cell at the other surface.

Varied carrier protein

One cell has many carrie rproteins

Saturation

When a carrier proteins becomes full, all the binding sites are full or saturated.

transport maximum (Tm)

For a substance that has reached its concentration saturation, this is called its transport maximum (Tm). T

renal threshold

which refers to the plasma concentration of a substance at which it begins to appear in the urine

Energy dependance:

Many carrier-mediated transports require ATP to actively move substances against their concentration gradients.

obligatory water reabsorption

water is “obliged” to follow the Na⁺, commonly phrased, “water follows salt”.

How much glucose, amino acids and vitamins are reabsorbed in PCT

100%

How much water and sodium is reabsorbed in PCT

67%

How much Cl- is reabsorbed in PCT

50%