Erection & Ejaculation: Endocrine Physiology

Overview

This lecture covers the physiology of erection and ejaculation, focusing on the male reproductive system. It outlines the processes involved, the anatomical structures, and the neurological pathways that facilitate these functions.

I) Erection

Anatomy of the Penis

• Components: Bulb, Shaft, Glans penis (tip)
• Main Structures:
  • Corpora Cavernosum (CC): Erectile tissue, spongy connective tissue filled with blood vessels
  • Corpora Spongiosum: Connective tissue lining the urethra, keeps urethra open during ejaculation

Stimulus for Erection

• Initial Stimuli:
  • Visual, tactile, thought, and olfactory
• Neurological Activation:
  • Activation of brain areas
  • S2-S4 region of the spinal column activates parasympathetic neurons
  • Pelvic nerve innervation of the corpora cavernosum

Biochemical Pathway

• Parasympathetic Response:
  • Secretion of acetylcholine
  • Triggers nitric oxide synthase (NOS)
  • Conversion of arginine into citrulline and nitric oxide (NO)
  • NO activates guanylyl cyclase, converting GTP to cGMP
  • cGMP activates K+ channels, hyperpolarizing cells

Resulting Vasodilatation

• Relaxation of smooth muscle cells
• Expansion of erectile tissue
• Blood engorgement leads to erection

Pharmacological Note

• Role of PDE5: Degrades cGMP
• Viagra (Sildenafil): Inhibits PDE5, maintaining cGMP levels

II) Ejaculation

Transition from Erection

• Neural Transition:
  • Cerebral cortex initiates sympathetic response
  • Inhibition of parasympathetic nervous system
  • Activation of sympathetic nervous system leading to ejaculation

Sympathetic Pathway Activation

• Spinal Activation: T12-T2 levels
• Postganglionic Neurons:
  • Synapse at the inferior mesenteric ganglion
  • Axons form the hypogastric plexus

Process of Ejaculation

• Sperm Movement:
  • Produced in seminiferous tubules, stored/matured in epididymis
  • Norepinephrine stimulates contraction, moving sperm through vas deferens
• Seminal Fluid Production:
  • Adrenergic receptor activation in seminal vesicles
  • Expulsion of seminal fluid into ejaculatory duct
  • Combination with sperm to form semen

Urethral Coordination

• Internal Urethral Sphincter:
  • Contracts to prevent semen reflux
• Skeletal Muscle Involvement:
  • Pudendal nerve innervates muscles
  • Muscle contractions propel semen

Conclusion of Ejaculation

• Orgasmic Peak
• Sympathetic Return: Restores flaccidity

III) Review Questions

1. What is the primary erectile tissue?
2. Function of the corpora spongiosum?
3. Chemical secreted by the parasympathetic neuron?
4. Enzyme in smooth muscle vessels?
5. Enzyme degrading cGMP?
6. Structure not part of the sympathetic system?
7. Where does sperm mature?
8. Main muscle for ejaculation?
9. Nerve for skeletal muscle in ejaculation?
10. Ion influx initiating ejaculation?

Answers

• Provided at the end of the lecture for self-assessment.