Intro to Renal Module Flashcards
1
Q
What is the major function of the kidney?
A
- To maintain homeostasis for a large number of solutes (i.e., Na, K, Cl, bicarbonate), minerals (calcium, phosphorous, magnesium), and water despite variations in endogenous production and dietary intake
- By changing its rate of excretion, kidney will keep total body content stable
2
Q
How is sodium involved in homeostasis?
A
- Restricted to extracellular space, so total body Na determines size of EC fluid volume (ECFV), which determines BP/blood volume
- Kidney links virtually every homeostatic function in some way or other to handling of Na+
- IC, EC osmolalities always the same (major osmole Na - ECFV and K - ICFV)
- Na+ influences total body water since it determines osmolality -> increased total body Na = increased osmolality, stimulating INC water intake via thirst + vasopressin secretion tells kidney to conserve water
- No Na+ -> No volume -> No BP -> No life
3
Q
What is the primary EC anion?
A
Cl - total body content kept normal by kidney (other major anion is bicarbonate)
4
Q
What is normal body water %?
A
- Human body about 60% water in M, 50% in F (lower skeletal muscle mass in females)
- Whether we drink 1 gallon or 2 cups of water, our kidney adjusts to maintain constant, normal total body water content
- By maintaining both total body solutes and total body water at constant, normal levels the kidney maintains osmolality at normal levels
5
Q
What is the key role of bicarbonate in maintaining homeostasis?
A
- Major ECFV buffer (anion)
- Key factor in acid-base balance
- Kidney involved in regulating plasma bicarbonate at a normal level which assists in keeping pH at a normal level (normal pH 7.40)
6
Q
What 3 waste materials does the kidney eliminate?
A
- Urea: byproduct of protein metabolism
- Creatinine: byproduct of muscle metabolism
- Uric acid: formed via breakdown of nucleic acids
7
Q
EPO
A
- Kidney is virtually the only source of erythropoietin
- Glycoprotein that stimulates bone marrow to INC red blood cell production (increased reticulocytes)
- Less functioning kidney mass -> less erythropoietin production -> low reticulocyte count w/a normocytic normochromic anemia
- Available as injectable medication, so anemia of chronic kidney disease is now treatable/reversible
8
Q
What are the major endocrine functions of the kidney?
A
- EPO
- 1-alpha hydroxylase
- Renin
- Para/autocrine:
1. Bradykinin
2. Prostaglandins
3. Endo factors: NO, endothelin
9
Q
1-alpha hydroxylase
A
- Kidney is virtually only source of the enzyme
- Final enzymatic step to produce 1,25 (OH) 2D3 or calcitriol**, which is the active form of **Vitamin D
- Less nephron function -> less of this enzyme -> less of active metabolite of Vitamin D
10
Q
Renin
A
- Kidney is the only source
- Produced at juxtoglomerular apparatus by specialized cells in the afferent arteriole
- Catalytic enzyme that starts off angiotensin-aldosterone cascade
11
Q
What are the paracrine/autocrine functions of the kidney?
A
- Bradykinin: vasodilatory, natriuretic substance
- Prostaglandin: production critical in auto-regulation of glomerular filtration rate (GFR), particularly the vasodilatory prostaglandins such as PGI2, PGE2
-
Endothelial factors (or substances produced by endothelial cells) such as:
1. Nitric oxide (vasodilator)
2. Endothelin: potent vasoconstrictor most commonly produced when there is an endothelial injury
12
Q
Blood pressure regulation
A
- Kidney the critical organ in maintaining BP b/c ECFV a func of total body Na content, and kidney dictates size of EC space & total body water
- Kidney is only supply of renin, controlling the RAAS axis: ang II potent vasoconstrictor and aldosterone promotes Na reabsorption
- Production of circulating vasodilatory substances, predominantly from renal medulla
- Almost every example of HTN comes back to func at kidney in one way or another -> HTN largely a kidney disease
13
Q
Other functions of kidney
A
- Catabolism of small peptide hormones, like insulin
1. DEC nephron mass = slower degradation of insulin -> diabetic w/chronic kidney disease’s exogenous or endogenous insulin lasts longer
2. Insulin requirements actually decline with progressive kidney disease. - Kidney can produce glc via gluconeogenesis when fasting -> can provide 25-33% of gluconeogenesis during fasting (very low GFR, i.e., kidney damage, with some INC incidence of fasting hypoglycemia -> also may be a marker of insulin resistance)
- Because it is an excretory organ, kidney is responsible for elimination of many meds
1. People with chronic kidney disease more susceptible to risk of high drug levels and potential toxicity with normal dosages
14
Q
Balance
A
- How kidney performs homeostasis
- Neutral: dietary intake plus endogenous production exactly matches excretion rate of the kidney (total body contents of the substance remains stable)
- Positive: intake + endogenous production > renal excretion rate (increased total body content)
- Negative: intake + endogenous production < renal excretion rate (leads to DEC total body content)
15
Q
Urine
A
- In any clinical setting, to know if kidney is working properly, examine urine content (substance/solutes)
- Example: pt by clinical examination looks like he has too much Na+ content in body (ECFV expansion) -> kidney should be eliminating Na+, so measure Na+ in urine to see if kidney is working properly (i.e. excreting sodium to eliminate excess body content)
- If total body excess, then kidney should be excreting: total body deficit- kidney should conserve
