Unit 7 - The Kidney LO's Flashcards
List and describe the six functions of the kidneys.
- Regulating ECF volume and blood pressure – through release or retention of water (maintains water balance).
- Regulating osmolarity of body fluids – maintains body fluids at 290 mOsm.
- Maintaining electrolyte balance by controlling levels of specific ions such as Na+, Cl-, K+, Ca2+, Mg2+, PO43-
- Homeostatic control of acid-base balance to maintain pH of body fluids – through reabsorption (retention) or secretion (release) of H+ and HCO3-.
- Excretion/elimination of wastes, such as
- end products of metabolism (urea, creatinine)
- foreign compounds (xenobiotics) such as drugs, pesticides and other environmental toxins. - Production of hormones – erythropoietin (stimulates RBC production) and renin (triggers pathway important for salt conservation).
Trace the path of a drop of urine from the kidney to the external environment.
Urinary system consists of
- 2 kidneys
- Nephrons filter plasma to form urine. Filtrate passes through the tube of the nephron, into collecting ducts, and then into the renal pelvis which is connected to the ureter.
- Blood is carried to the kidney through the renal artery and is drained from the kidney through the renal vein. - 2 ureters – carry urine to bladder
- 1 bladder – stores urine until micturition
- 1 urethra – passes urine out of body
Trace of a drop of blood from a renal artery, through the kidney, to the renal vein.
Blood is carried to the kidney through the renal artery and is drained from the kidney through the renal vein.
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Describe and diagram the anatomical relationship between the vascular elements and the tubular elements of the nephron. Identify the juxtaglomerular apparatus, macula densa, and granular cells.
- Vascular elements
- Two arterioles and two sets of capillaries between them (the renal portal system). A portal system moves blood between two capillary beds before returning it to the heart (most circulation patterns involve only a single capillary bed). - Tubular elements
- Each nephron is a twisted tube divided into different sections. Each section of the tube has specific functions that are carried out by the specific cell types located there.
Parts:
a. Renal corpuscle
b. Proximal convoluted tubule (PCT)
c. Descending thin loop of Henle
d. Ascending thin loop of Henle
e. Ascending thick loop of Henle
f. Distal Convoluted tubule (DCT)
g. Collecting Duct
Vascular and tubular elements come together to form the juxtaglomerular apparatus, a point of contact between the arterioles and the thick ascending limb of loop Henle.
Consists of:
1. Macula densa cells in thick ascending loop of Henle facing afferent and efferent arteriole.
- detect Na+ concentration of filtrate
2. Granular cells – surround afferent arteriole.
- secrete renin
List the three processes of the kidney and, for each, describe: the direction of fluid/solute movement, the location of the fluid/solute (internal vs. external), and whether the process is selective or nonselective.
- Glomerular Filtration
- Plasma in glomerular capillaries is filtered into the lumen of Bowman’s capsule to form the filtrate that will become urine
- Filtrate is similar in composition to plasma, but is almost protein free (only the smallest proteins can move past the filtration membrane into Bowman’s capsule).
- ~ 20% of plasma is filtered per pass (= filtration fraction) - Tubular Reabsorption
- SELETIVE movement of certain substances from the tubular lumen back into the venous system via peritubular capillaries.
- ~99% of filtrate is typically reabsorbed - Tubular secretion
- SELECTIVE transfer of certain substances from the peritubulr capillaries (and tubular cells) into the tubular lumen (i.e. into the filtrate). Provides a mechanism for rapid elimination of unwanted substances.
Describe and diagram fluid volume and osmolarity changes in each section of the nephron and describe the adaptive significance of the final volume and concentration of the urine.
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Diagram the filtration barriers a water molecule will pass as it travels from the blood into the lumen of the nephron and illustrate the anatomical structures and mechanisms by which filtration can be controlled.
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Describe the hydrostatic and osmotic pressures that contribute to glomerular filtration and indicate the direction of fluid movement favored by the net pressure.
- Glomerular capillary hydrostatic pressure (blood pressure), Pc
55
favours filtration - Plasma Colloid Osmotic Pressure 𝜋c
30
Opposes filtration - Bowman’s Capsule Hydrostatic Pressure, PB
15
Opposes filtration - Bowman’s Capsule Colloid Osmotic Pressure, 𝜋B
0
Favours filtration - Net filtration pressure (NFP +10 Favours (55 + 0) – (30+15) = mmHg filtration
Define GFR and give the average value for GFR.
The body uses homeostatic control to maintain glomerular filtration rate (GFR) within narrow limits despite short-term and long-term changes in mean arterial blood pressure.
In a healthy person, ~900 L of blood per day passes through the afferent arteriole and ~180 L/day (20%) is filtered into the nephrons, which is an average GFR of 125 mL/min.
Describe how GFR can be influenced by:
1) variable resistance in afferent and efferent renal arterioles, 2) myogenic and tubuloglomerular autoregulatory mechanisms,
3) hormonal control, and
4) neural control.
a. The Myogenic Response
- Increased pressure in the afferent arteriole induces vasoconstriction –> decreases flow into the glomerulus, decreasing Pc, and therefore GFR.
- Decreased pressure in the afferent arteriole induces vasodilation –> more blood into glomerulus, increases capillary hydrostatic pressure ( Pc) and therefore GFR).
b. Tubuloglomerular feedback
Changes in GFR affect the flow rate through the nephron (increasing GFR, increases flow rate of filtrate though nephron), and hence the [NaCl] moving past macula densa cells.
a. Sympathetic Nervous System (SNS) input
i. Stimulates 𝛼1-receptors on smooth muscle of afferent and efferent arterioles and causes vasoconstriction.
- Vasoconstriction in afferent arteriole reduces flow into glomerulus (decreases GFR)
- Vasoconstriction of efferent arteriole causes blood to back up in the glomerulus (increases GFR)
- Under moderate SNS activation, both balance and GFR is mostly held constant.
- SNS is most important in reducing GFR during severe acute disturbances (e.g. heavy exercise, severe
hemorrhage) .
Decreasing Kf, results in a decrease in GFR (filtration membrane is less permeable, so less filtrate forms).
b. Hormonal and Paracrine regulation
- Norepinephrine and epinephrine cause arteriolar
vasoconstriction - ↓GFR
- Angiotensin II causes vasoconstriction of efferent arteriole – helps to maintain GFR when pressure drops and flow through afferent arteriole is reduced
- Prostaglandins causes arteriolar dilation - ↑GFR
Describe and diagram specific examples of active transport, secondary active transport, passive reabsorption, and transcytosis mechanisms used by the kidney to accomplish reabsorption and distinguish between transepithelial transport and paracellular pathways.
Describe or create a generalized graph of the reabsorption of glucose in order to demonstrate how protein-mediated renal transport can reach saturation. Mark on the graph where transport maximum and renal threshold occur.
Determine GFR when given plasma inulin concentration and rate of inulin excretion and also explain why this relationship is valid.
Inulin (a carbohydrate found in some plants) can be used to estimate GFR since
- It is filtered but not reabsorbed, secreted, or metabolized, therefore the amount excreted = the amount filtered by the glomerulus.
- As a result Renal Clearance = GFR
Analyze renal handling of a substance and indicate if it is reabsorbed or secreted:
1) when given GFR, plasma concentration, and excretion rate of the substance, or
2) by comparing clearance of the substance to clearance of inulin or creatinine.
Apply the equation E = F – R + S to analyze renal handling of a substance.
