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Anatomy of penis and physiology of erection

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Anatomy of penis and physiology of erection

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Anatomy of penis and physiology of erection

  1. 1. ANATOMY OF PENIS & PHYSIOLOGY OF ERECTION Dr. Prateek Laddha Senior Resident Urology
  2. 2. ANATOMY • Penis - 2 corpora cavernosa & corpus spongiosm , encased with tunica, bucks fascia, dartos fascia & skin. • Function – Urinary and Sexual
  3. 3. SKIN OF PENIS • Penile skin :- Very mobile as its dartos fascia backing is very loosely attached to Buck fascia. Highly elastic, without appendages & fat. • Uncircumcised men:- The prepuce (foreskin) is the penile skin as it folds over the glans and attaches below the corona. • Glans penis skin is immobile as it is attached to the tunica albuginea below it.
  4. 4. FASCIA OVER PENIS DARTOS FASCIA (superficial fascia) • Continuation of colle's fascia in the perineum • Extends from base to prepuce • Loosely attached to skin & deeper buck’s fascia • Contains superficial arteries ,veins & nerves BUCKS FASCIA (deep fascia) • Tough elastic layer immediately adjacent to tunica albuginea. • The corpora cavernosa are surrounded by Buck fascia dorsally. • Buck fascia splits  corpus spongiosum ventrally. • Deep dorsal vein, Dorsal artery & Dorsal nerve are contained within bucks fascia. • Distally attached to glans.
  5. 5. TUNICA ALBUGINEA Bilayered • Inner layer - Circular, Intra cavernosal pillars • Outer layer - Longitudinally oriented, Absent between 5- 7° clock • Emissary veins – between two layers, outer layer compress emissary veins during erection. With Erection, are tightly stretched, and in the flaccid state they form an undulating meshwork Radiating from this inner layer are intracavernous pillars that act as struts to augment the septum and provide essential support to the erectile tissue The most vulnerable area is located on the ventral groove (between the 5 o’clock and 7 o’clock positions), where the longitudinal outer layer is absent; most prostheses tend to extrude here
  6. 6. CONTENTS OF TUNICA ALBUGINEA Fibrillar collagen (mostly type I but also type III) Collagen has a greater tensile strength than steel, it is unyielding. Elastin fibers • Elastin can be stretched up to 150% of its length. The elastin content allows tunical expansion and helps to determine stretched penile length.
  7. 7. LIGAMENTS • Suspensory— Arises from Buck fascia and consists of two lateral bundles and one median bundle, which circumscribe the dorsal vein of the penis. Main function - to attach the tunica albuginea of the corpora cavernosa to the pubis. Provides support for the mobile portion of the penis • Fundiform– Arises from Colles’ fascia and is lateral, superficial, and not adherent to the tunica albuginea of the corpora cavernosa
  8. 8. CORPORA CAVERNOSA • Paired cylinders & conglomeration of sinusoids • Sinusoids – separated by smooth muscle cells, connective tissues, collagen, arterioles, venules and terminal nerves • Crura - Proximal ends, covered by ischiocavernosus muscle, originate at the undersurface of the puboischial rami as two separate structures but merge under the pubic arch (distal to pubic symphysis) and remain attached up to the glans. CORPUS SPONGIOSUM • Single, contains urethra • Extends – bulb to glans • Sinusoids are larger • Tunica is thinner, lacks outer layer & intracorporeal struts • Bulb - fixed to perineal membrane , covered by bulbo spongiosus, narrows to form corpus spongiosum.
  9. 9. CORPORA
  11. 11. ARTERIAL SUPPLY • Bulbo urethral artery – urethra, spongiousm & glans • Cavernosal artery - cavernous sinus • Dorsal artery – below the bucks fascia & between dorsal nerves, supplies glans • Gives circulflex branches which encircle corpora and provide rich blood supply.
  12. 12. VENOUS DRAINAGE • Glans  Deep dorsal vein • C. Spongiosum Circumflex, urethral,& bulbar veins • C. Cavernosa  Mid & distal shafts to Deep dorsal vein • Proximal to cavernousal & crual veins • Skin Superficial dorsal vein in turn to saphenous veins
  13. 13. VENOUS DRAINAGE Subtunical venules Emissary veins Deep dorsal, circumflex & periurethral veins
  14. 14. LYMPHATIC DRAINAGE Prepuce & skin of the shaft Join at coronal level Sup. Inguinal nodes Glans &corporeal bodies - Join at base of penis Sup. Inguinal nodes Deep Inguinal nodes Pelvic nodes Erectile tissue Internal Iliac nodes
  16. 16. NERVE SUPPLY - SYMPATHETIC Sympathetic T11-L2 Sympathetic trunk Inf. Mesentric & Sup.Hypogastric plexus Hypogastric nerves Pelvic Plexus vasoconstriction, contraction of the seminal vesicles and prostate, and seminal emission NERVE SUPPLY :- PARA SYMPATHETICParasympathetic S2- S4 Pelvic splanchnic nerves (nervi erigentes) Pelvic plexus Preganglionic neurons synapse to give post ganglionic cavernous nerves. Produces vasodilataion
  17. 17. CNS • Modulatory effect Hypo thalamus, limbic system, ventral thalamus, tegmentum & latera substantial nigra • Medial pre optic area  recognize partner, integration of hormonal & sensory clues • Para ventricular nucleus & Hippocampus - erection
  18. 18. PENILE COMPONENTS AND THEIR FUNCTION DURING PENILE ERECTION Support corpus spongiosum and glans Contains and protects erectile tissue Provides rigidity of the corpora cavernosa Participates in veno-occlusive mechanism Pressurizes and constricts the urethral lumen to allow forceful expulsion of semen Regulates blood flow into and out of the sinusoids
  19. 19. MRI AND ANATOMY - Urethra - Corpora cavernosum - Corpus spongiosum - Smenial vesicals - Corpora cavernosum - Corpus spongiosum - Corpora cavernosum - Corpus spongiosum - Bulb of penis
  21. 21. HISTORICAL ASPECT • The first description of erectile dysfunction (ED) dates from about 2000 BC and was set down on Egyptian papyrus. Two types were described: natural (“the man is incapable of accomplishing the sex act”) and supernatural (evil charms and spells). • Hippocrates reported many cases of male impotence among the rich inhabitants of Scythia and ascribed it to excessive horseback riding • Aristotle - erection is produced by the influx of air. • Ambroise Paré - accurate account of penile anatomy and the concept of erection. • Hunter (1787), thought that venous spasm prevented the exit of blood • Wagner (1981) - increased arterial flow and decreased venous drainage during erection.
  22. 22. MECHANISM OF ERECTION Smooth muscles relax Artreial fiow increases Sunusoidial expansion Compression of sub tunical & emissary veins Reduction of flow  Erection In contrast to many other smooth muscles, corpus cavernosum smooth muscle is in a contracted state most of the time.
  23. 23. NEUROTRANSMITTERS IN ERECTION Cholinergic (Acetylcholine & NO) Smooth muscle relaxation, through inhibition of adrenergic nerves & release of nitric oxide Adrenergic (nor epinephrine) – Smooth muscle contraction & detumescence. NANC - Release of nitric oxide & accumulation of cGMP
  24. 24. MOLECULAR MECHANISM OF SMOOTH MUSCLE CONTRACTION 1. Cytosolic Free Calcium. 2. Rho Kinase Signaling Pathway (Calcium Sensitization Pathway) 3. Latch State: A Unique Characteristic of Smooth Muscle Contraction 4. Pathways Involving Inositol 1,4,5- Triphosphate, 1,2- Diacylglycerol, and Protein Kinase C
  25. 25. MOLECULAR MECHANISM OF CONTRACTION CYTOSOLIC INFLUX – Ca++ Calmodulin-4 Ca++ binds to myosin kinase Inhibit myosin actin interaction Smooth muscle contraction
  26. 26. MOLECULAR MECHANISMS IN SMOOTH MUSCLE RELAXATION 1. Cyclic Guanosine Monophosphate–Signaling Pathway. 1. Nitric Oxide 2. Carbon Monoxide 3. Hydrogen Sulfide 4. Natriuretic Peptides 5. Guanylyl Cyclase 6. Protein Kinase G. 2. Cyclic Adenosine Monophosphate–Signaling Pathway 1. Adenosine 2. Calcitonin Gene–Related Peptide Family. CGRP, 3. Prostaglandins 4. Vasoactive Intestinal Peptide 5. Adenylyl Cyclase 6. Protein Kinase A 3. Cross activation 4. Phosphodiesterase 5. Ion channels 6. Hyperpolarization of smooth muscles 7. Molecular Oxygen as a Modulator of Penile Erection
  27. 27. MOLECULAR MECHANISM Ca ++ Falls Ca++ dissociates from calmodulin Dissociates from Myosin kinase Relaxes muscle
  29. 29. SMOOTH MUSCLE PHYSIOLOGY:- • Relaxation of the cavernous smooth muscle is the key to penile erection. • NO released by nNOS contained in the terminals of the cavernous nerve initiates the erection process, whereas NO released from eNOS in the endothelium helps maintain erection. • On entering the smooth muscle cells, NO stimulates the production of cGMP. • cGMP activates PKG, which opens the potassium channels and closes the calcium channels. • Low cytosolic calcium favors smooth muscle relaxation. • The smooth muscle regains its tone when cGMP is degraded by PDE.
  30. 30. ROLE OF HORMONES • Androgens • Act on hypothalamus, important site for modulation of erection. • Modulate synaptic transmission, synthesis, uptake & release of neurotransmitters • Deficiency – loss of sexual interest, impaired seminal emission & reduced nocturnal erection
  31. 31. PHASES OF ERECTION • Flaccid phase • Latent or filling phase • Tumescent phase • Full erection phase • Skeletal or rigid erection phase • Detumescent phase
  32. 32. PHASES OF ERECTION Flaccid Phase: •Minimal arterial and venous flow •Blood gases values similar to venous blood Latent phase •Increased flow in int.pudendal artery during both systolic and diastolic phases •Decreased pressure in int.pudendal artery •Unchanged intracavernous pressure •Some elongation of penis Tumescen t phase • Rising intracavernous pressure until full erection achieved. • Penis shows more expansion and elongation with pulsation. • With rise in pressure arterial flow decrease and flow occurs only during systolic phases. Full erection phase • Intracavernous pressure rises 80-90% of systolic pressure • Int pudendal atrery pressure increase but remains slightly below systemic pressure • Arterial flow remains low but still remains higher than flaccid phase • Venous channels compressed but still higher than flaccid phase. Blood gas values approaches to that of arterial blood Skeletal or Rigid erection Phase: • Ischiocavernous mus contraction causes rise in pressure well above the systolic pressure lead to rigid erection • Almost no blood flows through cavernous artery • As the duration is short so no ischemia or tissue damage Detume scent Phase: • After ejection or cessation of erotic stimuli, sympathetic tonic discharge resumes. • Result - tonic contraction of smooth muscle which cause reduction in arterial flow and emptying of blood from sinusoids. • Penis returns to it flaccid length and girth.
  33. 33. TYPES OF ERECTION Nocturnal Occurs Cholinergic neurons in lateral Pontine tegmentum is activated whereas adrenergic neurons in locus coeruleus & steronergic neurons in midbrain are silent. This differential activation results in nocturnal erection in REM sleep. Psychogenic Fantasy or audiovisual stimuli. Impulses from brain spinal centers external genitalia Refluxogenic Tactile stimuli pudendal nerves sacral dorsal horn & dorsal gray commissure processed by interneurons parasympathetic cavernous & dorsal nerves
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Anatomy of penis and physiology of erection


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