MP

Autonomic, Renal & Urinary Systems – Comprehensive Study Notes

Autonomic Nervous System (ANS)

  • Big Picture

    • ANS = motor system we do NOT consciously control.

    • Supplies: \text{Cardiac muscle}, \text{Smooth muscle} (vessels + viscera), and glands.

    • Operates through a two-neuron chain (pre-synaptic ➜ ganglion ➜ post-synaptic) except in the adrenal medulla.

  • Functional Sub-divisions

    • Sympathetic (SNS) – “fight, flight, or fright”.

    • Parasympathetic (PNS) – “rest and digest / feed and breed”.

Sympathetic Division

  • Anatomical Key Points

    • Origin = thoracolumbar outflow T1-L2 (intermediolateral cell column of spinal cord gray matter).

    • Short pre-synaptic fibers, long post-synaptic fibers.

    • Two possible synapse sites:

    • Sympathetic chain (paravertebral) ganglia → targets above the diaphragm.

    • Pre-vertebral ganglia (a.k.a. collateral ganglia) for viscera below the diaphragm:

      • \text{Celiac}, \text{Superior mesenteric}, \text{Inferior mesenteric} (names match major abdominal arteries).

  • Three classic pathways for pre-ganglionic axons

    1. Enter chain, synapse at same level, exit via gray ramus.

    2. Enter chain, ascend/descend, synapse at a different level, exit via gray ramus.

    3. Enter chain, do NOT synapse, leave as a splanchnic nerve ➜ synapse in a pre-vertebral ganglion.

  • White vs. Gray Rami Communicantes

    • White rami = pre-synaptic fibers entering the chain ("white coat when you walk in the lab").

    • Gray rami = post-synaptic fibers leaving the chain ("dirty coat when you walk out").

    • White rami exist only T1-L2, gray rami exist at every spinal level (so sympathetics can be distributed body-wide).

  • Pre-synaptic splanchnic nerves (thoracic, lumbar, sacral)

    • Remain pre-synaptic until the pre-vertebral ganglion.

    • Supply foregut, midgut, hindgut & pelvic organs after synapse.

  • Adrenal (Suprarenal) Medulla Exception

    • Single pre-synaptic neuron passes through celiac ganglion, terminates on chromaffin cells.

    • Chromaffin cells release epinephrine / norepinephrine directly to the bloodstream → “endocrine branch” of the SNS.

Parasympathetic Division

  • Anatomical Key Points

    • Origin = craniosacral outflow.

    • Cranial portion: CN III,\;VII,\;IX,\;X.

    • Sacral portion: S2-S4 (pelvic splanchnic nerves).

    • Long pre-synaptic fibers, short post-synaptic fibers.

    • Ganglia located in or near the organ wall ("intramural" ganglia).

  • Major Routes

    • CN X (Vagus): carries PNS to thoracic viscera + abdominal foregut & midgut.

    • Pelvic splanchnic nerves (S2-S4): supply hindgut & pelvic viscera (distal \approx last third of colon, bladder, reproductive organs).

  • General Effects

    • Stimulate digestion, glandular secretion, defecation, urination, and sexual arousal (erection).

    • Inhibit heart rate & bronchial diameter (opposite of SNS).

Sympathetic vs. Parasympathetic – Rapid Comparison

  • Purpose

    • SNS: Energy mobilization (↑ HR, bronchodilation, pupil dilation, glycogenolysis).

    • PNS: Energy conservation (↑ GI motility, gland secretion, voiding, erection).

  • Origination Levels

    • SNS: T1-L2 (thoracolumbar).

    • PNS: Brainstem (CN III, VII, IX, X) + S2-S4 (craniosacral).

  • Fiber Lengths

    • SNS: short pre, long post.

    • PNS: long pre, short post.

  • Ganglia Location

    • SNS: paravertebral or pre-vertebral.

    • PNS: intramural.

  • Bodywide vs. Organ-specific

    • SNS: bodywide distribution (skin, vessels, viscera).

    • PNS: primarily visceral cavity + selected head glands.

Physiologic Endpoint Examples (Clinical Relevance)

  • Sympathetic Activation

    • Pupils dilate, salivation inhibited (dry mouth).

    • Heart rate & contractility ↑.

    • Bronchi dilate, respiratory rate ↑.

    • GI motility ↓, sphincters contract.

    • Ejaculation in males ("shoot").

  • Parasympathetic Activation

    • Pupils constrict, salivation ↑.

    • Heart rate ↓.

    • Bronchi constrict.

    • GI motility & secretion ↑.

    • Micturition & defecation facilitated.

    • Penile / clitoral erection ("point").

Referred Pain – Concept & Examples

  • Definition: Visceral pain perceived as originating from a somatic (body wall) location because visceral afferents share spinal cord pathways with somatic afferents.

  • Heart (Myocardial Infarction)

    • Visceral pain fibers enter at T1-T5 → brain interprets pain along dermatomes of left chest & medial left upper limb.

  • Appendicitis

    • Early pain via T10 = periumbilical region; later localizes to right lower quadrant as parietal peritoneum becomes involved.

  • Clinical Pearl: Always correlate dermatomal map with embryologic organ origin to predict referred pain zones.

Urinary System – Overview

  • Main Components

    1. Kidneys – produce urine ("work horses").

    2. Ureters – smooth muscle tubes from renal pelvis to bladder.

    3. Urinary Bladder – muscular reservoir (detrusor muscle).

    4. Urethra – conducts urine to exterior; markedly different length/segments in sexes.

  • Primary Functions

    • Filter blood plasma, excrete nitrogenous waste.

    • Regulate electrolyte/acid-base balance, blood volume & pressure.

    • Endocrine roles: \text{Erythropoietin}, \text{Renin}, Vitamin D activation.

Kidney Gross Anatomy

  • Position

    • Retroperitoneal on posterior abdominal wall.

    • Right kidney sits slightly lower (crowded by liver).

  • External Features

    • Renal capsule – thin, fibrous, shiny.

    • Hilum – entry/exit for vessels, nerves, ureter.

    • Renal sinus – fat-filled space containing branching vessels & renal pelvis.

  • Internal Parenchyma

    • Renal cortex = outer \tfrac{1}{5}.

    • Renal medulla = inner \tfrac{4}{5} composed of renal pyramids.

    • Apex of pyramid = renal papilla → first grossly visible urine drips.

    • Renal columns = cortical tissue between pyramids.

  • Collecting System (Minor ➜ Major ➜ Pelvis)

    • Each papilla drains into a minor calyx.

    • Minor calyces merge → major calyx (2-3 per kidney).

    • Majors unite → renal pelvis → narrows as ureter.

Renal Vasculature (Arterial Pathway)

\text{Renal a.} \;\to\; \text{Segmental a.} \to \text{Interlobar a.} \to \text{Arcuate a.} \to \text{Interlobular (cortical radiate) a.} \to \text{Afferent arteriole} \to \text{Glomerulus} \to \text{Efferent arteriole}

  • Mnemonic: Rats Skip In All Igloos After Gulping Espresso.

  • Venous return mirrors arteries in reverse → renal vein ➜ IVC.

Nephron Micro-Anatomy & Physiology

  • Two Structural Parts

    1. Renal corpuscle (cortex only)

    • Glomerulus – tuft of fenestrated capillaries.

    • Bowman’s (glomerular) capsule – parietal + visceral layers.

    1. Renal tubule

    • Proximal convoluted tubule (PCT) – major reabsorption site.

    • Loop of Henle – descending & ascending limbs (medullary salt gradient).

    • Distal convoluted tubule (DCT) – hormone-regulated fine-tuning.

    • Collecting duct – not part of nephron proper; multiple nephrons empty here ➜ papilla.

  • Processes

    • Filtration (in corpuscle): plasma ➜ filtrate.

    • Reabsorption: substances reclaimed from filtrate to blood (e.g.
      \text{H}_2\text{O}, \text{Na}^+, glucose).

    • Secretion: additional waste/ions moved from blood to tubular fluid (e.g.
      \text{K}^+, \text{H}^+, drugs).

Ureters

  • Muscular Tubes (~25-30 cm) using peristalsis to propel urine.

  • Retroperitoneal entire length.

  • Enter bladder obliquely, forming functional one-way flap valves (prevent reflux during bladder contraction).

Urinary Bladder

  • Location: True pelvis, posterior to pubic symphysis.

  • Layers: mucosa, detrusor (smooth) muscle, adventitia/serosa.

  • Trigone – triangular area b/w ureteric orifices & internal urethral orifice; clinically important (infections).

Urethra & Pelvic Floor Openings

  • Female: short (~4 cm); single function (urinary).

  • Male: longer (~20 cm) with three named parts (prostatic, membranous, spongy) – dual urinary & reproductive role.

  • Pelvic diaphragm apertures

    • Male: 2 (urethra, anus).

    • Female: 3 (urethra, vagina, anus).

Integration & Study Tips

  • Link ANS to Vasculature: Sympathetic tone maintains resting vascular resistance; renal arterioles constrict under SNS (low-flow state).

  • Embryology tie-in: Craniosacral vs. thoracolumbar origins mirror neural crest migration routes discussed in previous lectures.

  • Clinical Ethics: Recognize MI referred pain to avoid dismissal of "indigestion" complaints; timely diagnosis saves myocardium.

  • Practical Application: Palpate costovertebral angle tenderness → possible renal pathology; understand dermatomal overlap to differentiate renal colic from LBP.

Quick Reference Cheat-Sheet

  • Sympathetic: T1-L2 | short-pre | chain/pre-vertebral ganglia | bodywide | "fight or flight".

  • Parasympathetic: CN III, VII, IX, X + S2-S4 | long-pre | intramural ganglia | viscera-focused | "rest & digest".

  • Kidney Flow: Papilla → Minor calyx → Major calyx → Pelvis → Ureter → Bladder → Urethra.

  • Renal Artery Branching: Renal → Segmental → Interlobar → Arcuate → Interlobular → Afferent arteriole.

Use these bullet-points as a full replacement for the original transcript when revising for the exam.