Ch.14 Urinary System

Human Physiology

The ___ maintain the stability and composition of the ECF. They contribute to homeostasis. They control electrolyte and water balance of the ECF, plus urinary output. If the ECF has an excess of water or electrolytes, the ___ eliminate the excess. If there is a deficiency of these substances, the ___ can reduce the loss of these from the body.

kidneys

Other functions of the kidneys include: maintaining the proper osmolarity of body fluids, maintaining proper plasma volume, helping to maintain proper acid-base balance, excreting wastes of body metabolism, excreting many foreign compounds, producing ___ and renin, converting vitamin D to an active form

erythropoietin

Review general anatomy of kidney, renal artery, renal vein, and such

Review general anatomy of kidney, renal artery, renal vein, and such

The nephron is the functional unit of the kidney. It is the smallest unit that can perform all of the functions of the kidney. Each kidney has about one ___ nephrons.

million

___ is the outer region of the kidney formed by the nephrons, and looks granular

renal cortex

___ is the inner region of the kidney formed by the nephrons, and is made up of renal pyramids

renal medulla

___ are the striated triangle portion that make up the renal medulla

renal pyramids

The nephrons are arranged through the cortex and medulla of the kidney. Each nephron consists of a vascular component and a ___ component.

tubular

The ___ is a ball-like tuft of capillaries

glomerulus

The ___ component is the dominant portion of the nephron: Water and solutes are filtered through the glomerulus as blood passes through it. From the renal artery, inflowing blood eventually passes through afferent arterioles. Each afferent arteriole delivers blood to the glomerulus. The efferent arteriole transports blood from the glomerulus. The efferent arteriole breaks into peritubular capillaries. They surround the tubular part of the nephron. They are involved with tubular changes between this part of the nephron and the blood. The peritubular capillaries join into venules which transport blood into the renal vein.

vascular

The ___ part of the nephron is a hollow tube with different regions.  Fluid (filtrate) passes through the nephron. It begins with the Bowman’s capsule which fits around the glomerulus. Filtered fluid passes from the Bowman’s capsule into the proximal tubule. It lies entirely in the cortex. The next segment is the loop of Henle. Fluid passes through its descending limb and is ascending limb next. Tubular and vascular cells at this point form a juxtaglomerular apparatus. From the descending limb, the next tubular part is the distal tubule. The distal tubule empties into the collecting duct

tubular

The loop of Henle and collecting duct are found in the ___ of the kidney.

medulla

The cortical and juxtamedullary nephrons (with vasa recta) are distinguished by their location (___ or medulla) and length.

cortex

Draw book nephron diagram

Draw book nephron diagram

Draw slides nephron diagram

Draw slides nephron diagram

The three basic processes of the ___ are glomerular filtration, tubular reabsorption, and tubular secretion to form urine. (p.515-537)

nephrons

___ is the first process. A protein-free plasma is filtered from the glomerulus into the Bowman’s capsule. Blood cells are not normally filtered. Normally about 20% of the plasma is filtered. ___ is produced at the rate of 125 ml per minute (180 liters per day).

glomerular filtration

By ___, filtered substances move from the inside of the tubular part of the nephron into the blood of the peritubular capillaries. The reabsorption rates of most substances are very high.

tubular reabsorption

___ is a selective process by which substances from the peritubular capillaries enter the lumen of the nephron tubule. The 80% of the plasma not filtered passes into the efferent arteriole and through the peritubular capillaries.

tubular secretion

Draw basic three processes graph (slides & p.517)

Draw basic three processes graph (slides & p.517)

Kidney Urine Formation: Filtration – Reabsorption – Secretion

urine

Draw gummy slide exclusive diagram (s.3)

Draw gummy slide exclusive diagram (s.3)

Substances filtered from the glomerulus pass through three layers. They are wall of the glomerular capillaries, the basement membrane, and the inner layer of the Bowman’s capsule. (p.517-518)

membrane

The ___ is more permeable to water and solutes compared to other body capillaries.

glomerular membrane

The ___ is a gelatinous layer between the (wall of) glomerulus (capillaries) and (inner layer of) Bowman’s capsule.

basement membrane

The inner layer of the Bowman’s capsule contains podocytes that encircle the ___. Normally blood cells and plasma proteins are not filtered.

glomerulus tuft

Draw Layers of the glomerular membrane diagram

Draw Layers of the glomerular membrane diagram

Glomerular filtration occurs by the interaction of forces. (p.518-519)

interaction

The ___ is the result of the blood pressure pushing on the inside of the capillary wall (e.g., 55 mm Hg). As blood pressure increases, the ___ tends to increase. As the blood flowing through the glomerulus works against a small-diameter efferent arteriole, this also increases this pressure.

glomerular capillary pressure

The ___ is due to the retention of plasma proteins in the blood of the glomerulus. The concentration of water is higher in the glomerulus, as the proteins are absent there. Water tends to return to the blood in the glomerulus by osmosis (30 mm Hg).

plasma-colloid osmotic pressure

There is also a (Bowman's capsule) ___ tending to move fluid from the Bowman’s capsule into the glomerulus (15 mm Hg)

hydrostatic pressure

The net filtration pressure is an interaction of three pressures. From the previous examples: 

The net pressure = glomerular blood pressure - (plasma-colloid osmotic pressure + Bowman’s capsule hydrostatic pressure). Therefore: 55 - (30 +15) = 10. Thus, the net filtration pressure is 10 mm Hg. (p.519-520)

net filtration pressure

The ___ is the product of:  properties of the glomerular membrane times the net filtration pressure. The properties include the glomerular surface for penetration and the permeability of the glomerular membrane (p.520-521

glomerular filtration rate (GFR)

Controlled adjustments in the GFR are mainly due to changes in the glomerular capillary blood pressure. Although changes in the plasma-colloid osmotic pressure and Bowman’s capsule hydrostatic pressure can change the GFR, these are not controlled adjustments of the GFR.

glomerular capillary

A higher arterial blood pressure supplying the glomerulus, and more constriction of the efferent arterioles, can increase the GFR. For example, from the previous example, if the glomerular blood pressure increases from 55 to 60: 

60 - (30 + 15) = 15 

(not 10 as in the previous example). Note that the net filtration pressure (and GFR) changes.

arterial blood pressure

Draw direction effect of arterial blood pressure diagram (slides & p.520)

Draw direction effect of arterial blood pressure diagram (slides & p.520)

___ is the process of preventing inadvertent changes in GFR via intrinsic regulatory mechanisms initiated by the kidneys. By ___ the kidneys regulate the GFR by factors within these organs. They mainly alter the caliber of the afferent arterioles. If the GFR rises by increased arterial pressure, the afferent arterioles constrict. This lowers the GFR. If the GFR decreases, the afferent arterioles dilate

autoregulation

The mechanisms for autoregulatory responses are ___ (responding to changes in the nephron’s vascular component) and a tubuloglomerular feedback mechanism. This feedback occurs by sensing changes in flow in the nephron’s tubular component.  These two mechanisms work in unison to autoregulate the GFR. They prevent inappropriate changes in the GFR

myogenic

Uncontrolled shifts in the GFR can lead to fluid and ___ imbalances. Changes outside a range in the arterial pressure cannot be compensated by autoregulation

electrolyte

Draw adjustment of afferent arteriole diagram (slides & p.521)

Draw adjustment of afferent arteriole diagram (slides & p.521)

Extrinsic ___ control can adjust the GFR: They can override the autoregulatory mechanisms. If arterial blood pressure drops, most arterioles in the body constrict by the baroreceptor reflex. These include the afferent arterioles supplying the glomeruli. The afferent arterioles constrict by sympathetic innervation. Less blood flows through the glomeruli, lowering the blood pressure in these capillaries. The resultant decrease in the GFR reduces urine volume. They help to conserve plasma volume, increasing blood pressure. If blood pressure is elevated, the direction of these responses is reversed. The responses in the kidneys by the baroreceptor reflex is part of responses throughout the body for the long-term adjustment of blood pressure. (p.522)

sympathetic

The GFR can be influenced by changes in the ___. This ___ is not constant but is subject to physiological control. The ___ depends on surface area and the permeability of the glomerular membranes. Both can be modified by contractile activity within the membrane. (p.523)

filtration coefficient

The kidneys receive _% of the cardiac output. The total blood flow through the kidneys average 1,140 ml per minute. If the cardiac output is 5 liters, this figure is 22 % of the cardiac output. This kidneys need to receive this large blood flow to monitor and control the extracellular fluid. (p.524)

20 to 25

Draw total cardiac output graphic (s.6)

Draw total cardiac output graphic (s.6)

___ are what the efferent arteriole subdivides into. Supply the renal tissue with blood and are important in exchanges between the tubular system and blood during conversion of the filtered fluid into urine

peritubular capillaries

By tubular reabsorption filtered substances are transferred from the tubular lumen to the peritubular capillaries. This process is highly selective and variable. The return of substances to the blood is needed to maintain the composition of the ___. Only excesses of materials are eliminated. Reabsorption rates are high: 124 of 125 ml of filtered fluid per minute, 99% for water, 100% for glucose, and 99.5% for salt. (p.524) (figure 14-14 for visual)

ECF

___ is the interior space of a hollow organ or tube

lumen

___ meaning the base and sides of a cell or tissue

basolateral

Tubular reabsorption involves ___. The single layer of epithelial cells of the nephron tubule have a luminal membrane and a basolateral membrane facing the interstitial spaces between the tubule and peritubular capillaries.  By ___ a reabsorbed substance must cross the tubule wall, enter the interstitial fluid, and pass through the wall of the peritubular capillaries, entering the blood. (p.525-?)

transepithelial transport

There is passive reabsorption and active reabsorption, requiring the expenditure of energy

expenditure

Sodium reabsorption occurs at a high rate. 67% occurs in the ___. The reabsorption of glucose, amino acids, water, chloride ions, and urea are linked to this.

proximal tubule

The reabsorption of sodium in the ___ plays a role in the production of varying concentrations and volumes of the urine

loop of Henle

In the ___, sodium reabsorption depends on hormonal control.

distal tubule

Draw steps of transepithelial transport diagram (p.525)

Draw steps of transepithelial transport diagram (p.525)

Draw Reabsorption in the Proximal Convoluted Tubule diagram (s.7)

Draw Reabsorption in the Proximal Convoluted Tubule diagram (s.7)

Draw Renin-angiotensis-aldosteron system (RAAS) diagram (p.528 & s.8)

Draw Renin-angiotensis-aldosteron system (RAAS) diagram (p.528 & s.8)

___ is the transfer of substances from the peritubular capillaries into the tubular lumen. Hydrogen and potassium ions, along with organic anions, are ___(-ed).

tubular secretion

Tubular secretion: Hydrogen ions are secreted and removed from the blood to oppose acidosis

acidosis

Tubular secretion: Potassium is almost completely reabsorbed in the ___

proximal tubule

___ secretion is controlled by aldosterone in the distal tubule and collecting duct. It is variable and subject to regulation.

potassium

Draw potassium ion secretion diagram (s & p.535)

Draw potassium ion secretion diagram (s & p.535)

Draw summary of molecules reabsorbed and secreted graphic (slides)

Draw summary of molecules reabsorbed and secreted graphic (slides)

A rise in plasma potassium stimulates aldosterone from the ___. A fall in plasma secretion stimulates aldosterone secretion by the renin -angiotensin pathway.

adrenal cortex

The distal parts of the nephron can secrete either potassium or ___ ions in exchange for reabsorbed sodium

hydrogen

Regulating potassium in the ECF is important for membrane excitability. A rise in potassium ECF can ___ nerve and muscle cell membranes.

depolarize

The secretion of organic anions and cations helps eliminate foreign compounds. For example, some of these anions are bound to ___ and cannot be filtered. Tubular secretion eliminates them from the body. Foreign compounds include food additives. (p.536)

plasma proteins

___ is the volume of plasma cleared of a particular substance per minute. It is the volume of plasma from which the substance is removed, not the amount of the substance removed. (p.537)

plasma clearance

If a substance is filtered but not reabsorbed or secreted, its plasma clearance rate ___ the GFR. Inulin is an ideal substance, injected into the body, to compute a clearance rate. Creatine is an endogenous substance that is only filtered

equals

If a substance is filtered and reabsorbed, but not secreted, its plasma clearance rate is always ___ than the GFR. For glucose, it is zero, as the reabsorption of glucose is 100 percent

less

If a substance is filtered and secreted, but not reabsorbed, its plasma clearance rate is always ___ than the GFR

greater

Depending on the body’s state of ___, the kidneys secrete urine of varying concentrations. Too much water in the ECF establishes a hypotonic ECF. A water deficit establishes a hypertonic ECF. A large, vertical osmotic gradient is established in the interstitial fluid of the medulla (from 100 to 1200 mosm/liter to 1200 mosm/liter). This increase follows the hairpin loop of Henle deeper and deeper into the medulla. This osmotic gradient exists between the tubular lumen and the surrounding interstitial fluid. (p.539-540)

hydration

Comparing the descending and ascending limbs of the loop of Henle: The descending ling is highly permeable to water but does not extrude sodium for reabsorption.

extrude

Comparing the descending and ascending limbs of the loop of Henle: The ascending limb actively transports NaCl out of the tubular lumen into the surrounding interstitial fluid. It is impermeable to water. Therefore, water does not follow the salt by osmosis.

impermeable

There is a countercurrent flow produced by the close proximity of the two limbs. The ascending limb produces an interstitial fluid that becomes hypertonic to the ascending limb. It does this by pumping out sodium ions. Water does not follow. This interstitial fluid faces against the flow of fluid (countercurrent) in the descending limb, attracting the water by osmosis for reabsorption

hypertonic

The medullary vertical osmotic gradient is established by this countercurrent multiplication. (p.540-541)

multiplication

Draw vertical osmotic gradient diagram (s & p.540)

Draw vertical osmotic gradient diagram (s & p.540)

___-controlled, variable water reabsorption occurs in the final tubular segments. (p.541-546)

vasopressin

_% of water reabsorption is obligatory in the proximal tubule. In the distal tubule and collecting duct it is variable, based on the secretion of ADH

65

The secretion of vasopressin ___ the permeability of the tubule cells to water. An osmotic gradient exists outside the tubules for the transport of water by osmosis.

increases

___ is produced in the hypothalamus and stored in the posterior pituitary. The release of this substance signals the distal tubule and collecting duct, facilitating the reabsorption of water. ___ works on tubule cells through a cyclic AMP mechanism.

vasopressin

During a water ___, the secretion of vasopressin increases. This increases water reabsorption.

deficit

During a water ___, the secretion of vasopressin decreases. Less water is reabsorbed. More is eliminated

surplus

The ___ allows blood to the medulla and enter the renal vein at a level that is isotonic to the incoming arterial blood. These vessels loop back through the concentration gradient in the interstitial fluid in reverse

vasa recta

The water and solute reabsorption versus excretion are only partially coupled. In tubular segments that are permeable to water, ___ is always accompanied by comparable water reabsorption by osmosis.

solute reabsorption

The water and solute reabsorption versus excretion are only partially coupled. ___ is always accompanied by comparable water excretion because of osmosis

solute excretion

A loss or gain of pure water that is not accompanied by a comparable solute deficit or excess in the body leads to changes in ___ osmolarity

ECF

Renal failure has far-reaching consequences in the body. These include: infectious organisms retained in the body, the accumulation of toxic agents, inappropriate immune responses, obstruction of ___ flow, and an insufficient renal blood supply

urine