Lecture 20: Renal 3 — Reabsorption, Secretion & Excretion -

What are the key details about basic renal processes overview?

Glomerular filtration; Glomerulus to glomerular capsule; Reabsorption; Tubules to peritubular capillaries; Secretion; Peritubular capillaries to tubules; Excretion; Tubules to eventually out of body; 180 L / day; 1.5 L / day

What does tubular reabsorption explain (part 1)?

From tubules (filtrate) to peritubular capillaries (blood); After Filtration, filtrate is in the Proximal Convoluted Tubule (PCT); Certain components are reabsorbed to peritubular capillaries

What does tubular reabsorption explain (part 2)?

Capillaries follow closely the renal tubule; Net Pressure gradient favors reabsorption; NRP = HPpc - OPpc - HPpct - OPpct; NRP = 10 - 30 = - 20 mmHg; → Reabsorption favored; HP, hydrostatic pressure; OP, oncotic pressure; pc,

What does tubular reabsorption explain (part 3)?

peritubular capillary; pct, proximal convoluted tubule

What does tubular reabsorption explain (part 1)?

Allows to regulate homeostasis; The peritubular capillaries reabsorb useful substances; Water (65%); Glucose (100%); Amino acids (100%); Ions (variable); Mostly localized in proximal; convoluted tubule → simple

What does tubular reabsorption explain (part 2)?

cuboidal epithelium w/microvilli; Some is passive, most is active; Rapid elimination of foreign; substances through filtration,; without a mechanism to reabsorb

What does tubular reabsorption explain (part 1)?

PCT reabsorbs approx; 67% of filtrate; thin Descending Limb; f LoH is permeable t; H2O, impermeable t; ions (Na+Cl–); Thick Ascending Limb; (TAL) of LoH is; permeable to ions,; impermeable to H2O.; DCT and CD depend on; ANP and ADH for

What does tubular reabsorption explain (part 2)?

reabsorption of NaCl,; K+, and H2O.; Atrial Natriuretic; peptide acts here; ANP, Atrial Natriuretic Peptide;; ADH, AntiDiuretic Hormone (aka; Vasopressin, Vp)

What does (pct) tubular reabsorption explain (part 1)?

Osmolarity: Filtrate = ECF (ISF, IVF); to move solute → Active transport:; concentration / electrochemical gradients; PCT lumen; (blood); A– (HCO3; Cl–, Pi, aa); K+, Ca2+, aa; Urea, Glc,; Secondary Active; Primary Active; Passive

What does (pct) tubular reabsorption explain (part 2)?

Foreign / toxic; substances; Na+/K+ ATPase pump; Transporters:; NHE, ENaC; SGLT (Na+/Glc coTrR); [Na+]; [K+]

What does tubular reabsorption/secretion explain (part 1)?

Reabsorption and secretion of ions and water help; regulate the osmolarity of ECF.; What is not needed must be excreted through the tubule.; Regulation of Blood Volume and Blood pressure; depend on:

What does tubular reabsorption/secretion explain (part 2)?

reabsorption or secretion of H2O; reabsorption or secretion of ions, particularly of Na+; ⇒ “water follows solutes”); Regulation of ECF osmolarity and pH depends on:; reabsorption or secretion of Na+, K+, Cl–, others

What does tubular reabsorption/secretion explain (part 3)?

reabsorption or secretion of H+, HCO3; –, P(CO2); What mechanisms regulate these processes?; What signals and cells are involved?

What does tubuloglomerular feedback & raas explain (part 1)?

%NaCl (& H2O) reabsorbed @PCT; NaCl delivery @ Macula; densa (JGA); paracrine secretion; Vasoconstriction; HPgc; Aff arteriolar BF; Arterial pressure; Renin; Angiotensin II; HPgc; Eff arteriolar BF; Vasoconstriction; Blood volume; H2O follows

What does tubuloglomerular feedback & raas explain (part 2)?

Na transporters; @DCT, @CD; Aldosterone

What are the key details about tubuloglomerular feedback & raas?

%NaCl (& H2O) reabsorbed @PCT; Arterial pressure; T/F?; When arterial pressure decreases,; I expect GFR to decrease.

What are the key details about tubuloglomerular feedback & raas?

%NaCl (& H2O) reabsorbed @PCT; NaCl delivery @; Macula densa (JGA); Arterial pressure (proxy GFR); low flow and; low osmolality; paracrine secretion; Vasoconstriction; HPgc; Aff arteriolar BF; local

What does tubuloglomerular feedback & raas explain (part 1)?

%NaCl (& H2O) reabsorbed @PCT; NaCl delivery @; Macula densa (JGA); paracrine secretion; Vasoconstriction; HPgc; Aff arteriolar BF; local; Arterial pressure (proxy GFR); T/F?; When GFR decreases,; I expect a mechanism that

What does tubuloglomerular feedback & raas explain (part 2)?

increases Hydrostatic Pressure in; the glomerular corpuscle (HPgc).

What does tubuloglomerular feedback & raas explain (part 1)?

%NaCl (& H2O) reabsorbed @PCT; NaCl delivery @; Macula densa (JGA); Arterial pressure (proxy GFR); paracrine secretion; Vasoconstriction; HPgc; Aff arteriolar BF; localX; T/F?; When GFR decreases,; I expect a mechanism that

What are the key details about tubuloglomerular feedback & raas?

%NaCl (& H2O) reabsorbed @PCT; NaCl delivery @; Macula densa (JGA); Arterial pressure (proxy GFR); paracrine secretion; Vasoconstriction; HPgc; Aff arteriolar BF; localX; T/F?; The patient’s BP,; BV and GFR will; now return t; normal.

What does tubuloglomerular feedback & raas explain (part 1)?

%NaCl (& H2O) reabsorbed @PCT; NaCl delivery @; Macula densa (JGA); Arterial pressure (proxy GFR); paracrine secretion; Vasoconstriction; HPgc; Aff arteriolar BF; localX; T/F?; The patient’s BP,; BV and GFR will; now return t; normal.; Renin (JG)

What does tubuloglomerular feedback & raas explain (part 2)?

Angiotensin II; Systemic; vasoconstriction; Systemic; blood pressure

What does tubuloglomerular feedback & raas explain (part 1)?

%NaCl (& H2O) reabsorbed @PCT; NaCl delivery @; Macula densa (JGA); Arterial pressure (proxy GFR); paracrine secretion; Vasoconstriction; HPgc; Aff arteriolar BF; localX; Renin (JG); Angiotensin II; Systemic; vasoconstriction; Systemic

What does tubuloglomerular feedback & raas explain (part 2)?

blood pressure; T/F?; If ↘ Syst BP; → HResp: ↗ BV.; HResp = homeostatic response

What does tubuloglomerular feedback & raas explain (part 2)?

blood pressure; T/F?; If ↘ Syst BP; → HResp: ↗ BV.; HResp = homeostatic response; Aldosterone

What does tubuloglomerular feedback & raas explain (part 2)?

blood pressure; T/F?; If ↘ Syst BP; → HResp: ↗ BV.; Aldosterone; Blood volume; Na+, H2O; reabsorbed; @DCT, @CD

What does tubuloglomerular feedback & raas explain (part 2)?

blood pressure; Aldosterone; Blood volume; Na+, H2O; reabsorbed; @DCT, @CD; T/F?; The patient’s BP, BV and GFR; will now return to normal.

What does summary on intrinsic and extrinsic explain (part 1)?

REGULATION OF GFR; GFR is tightly regulated to serve 2 potentially opposing needs:; maintain GFR (if MAP range: 80-180 mmHg); → intrinsic autoregulation: myogenic and tubuloglomerular

What does summary on intrinsic and extrinsic explain (part 2)?

maintain systemic BP (for sustained blood perfusion to vital; rgans) and ultimately body fluid volume (BV); → extrinsic regulation: nervous (SyNS) and endocrine; (Angiotensin II, Aldosterone, ADH) systems

What does summary on intrinsic and extrinsic explain (part 3)?

In extreme changes of MAP (BP): Extrinsic >> intrinsic

What are the key details about raas for bp regulation?

RAAS: RENIN, ANGIOTENSIN II; & ALDOSTERONE SYSTEM

What are the key details about reabsorption of hco3?

–: PH BUFFER; CO2 + H2O ⇄ H2CO3 ⇄ H+ + HCO3; – (by Carbonic Anhydrase); LUMEN; PCT cell

What does tubular secretion explain (part 1)?

From the peritubular capillaries to the renal tubules; (opposite of reabsorption); Discrete transport of selected substances:; Potassium → membrane excitability; Hydrogen ions → pH; Phosphate → PTH and Ca2+ homeostasis

What does tubular secretion explain (part 2)?

Choline; Creatinine; Penicillin; Materials remaining in the renal tubule move toward the ureter,; with no additional capacity of reabsorption/secretion

What does tubular secretion: hydrogen ion balancing explain (part 1)?

Type A intercalated cells; function in acidosis:; H+ is excreted; HCO3; –, K+ are reabsorbed; Type B intercalated cells; function in alkalosis:; H+ is reabsorbed; HCO3-, K+ are secreted; [H+] high; Lumen; Collecting; Duct; InterStitial

What does tubular secretion: hydrogen ion balancing explain (part 2)?

Fluid (ISF); H+ is secreted by the PCT, DCT, CD (intercalated cells).; H+ secretion depends on the acidity of body fluids

What does h+ is secreted by the pct, dct, cd (intercalated cells) explain (part 1)?

H+ secretion depends on the acidity of body fluids; Type B intercalated cells; function in alkalosis (basic):; H+ is reabsorbed; HCO3; –, K+ are secreted; [H+] high; [H+] low; Type A intercalated cells; function in acidosis:

What does h+ is secreted by the pct, dct, cd (intercalated cells) explain (part 2)?

H+ is excreted; HCO3; –, K+ are reabsorbed; Lumen; Collecting; Duct; InterStitial; Fluid (ISF); Lumen; Collecting; Duct; InterStitial; Fluid (ISF); A (alpha) and B (beta) cells; are symmetrically inverted!!

What does h+ is secreted by the pct, dct, cd (intercalated cells) explain (part 3)?

TUBULAR SECRETION: HYDROGEN ION BALANCING

What are the key details about excretion rate?

Amount of substance excreted = amount; filtered – amount reabsorbed + amount; secreted; Obligatory urine (approx 500 mL / day) t; excrete toxic waste (even when dehydrated).

What does concept reviews explain (part 1)?

99% of the volume of the filtrate is reabsorbed. 1.8L are; excreted as urine/day.; The bulk of the reabsorption occurs at the PCT (100% Glc,; aa, HCO3–; 65% water, K+, Na+, Cl–)

What does concept reviews explain (part 2)?

Renin promotes the activation of Angiotensin II: major; systemic vasoconstrictor, induces expression of aldosterone; → increase BP and BV; Aldosterone increases Na+/K+ ATPase activity → ↗Na+

What does concept reviews explain (part 3)?

reabsorption → water follows salt → ↗ water reabsorption;; also excretes K+; If high osmolarity → Anti-diuretic Hormone (= vasopressin); acts on CD by increasing Aquaporin expression at apical

What does concept reviews explain (part 4)?

region of principal cells → ↗ water reabsorption; If preload stretches atria (= high BV, BP) → Atrial; Natriuretic Hormone → decrease Na+/K+ ATPase activity; → excrete Na+ → water follows Na+ → ↗urine excretion