Anatomy of penis and physiology of erection

1. ANATOMY OF PENIS
&
PHYSIOLOGY
OF
ERECTION
Dr. Prateek Laddha
Senior Resident
Urology

2. ANATOMY
• Penis - 2 corpora cavernosa &
corpus spongiosm , encased
with tunica, bucks fascia,
dartos fascia & skin.
• Function – Urinary and
Sexual

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. 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. 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. 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. 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. 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. CORPORA

10. ARTERIAL SUPPLY
INTERNAL
PUDANDA
L
Bulbo
Urethral
Cavernosal
Dorsal
COMMON
PENILE

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. 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. VENOUS DRAINAGE
Subtunical
venules
Emissary veins
Deep dorsal,
circumflex &
periurethral veins

15. 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. NERVE SUPPLY
SOMATIC

17. 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

18. 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

19. 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

20. MRI AND ANATOMY
- Urethra
- Corpora cavernosum
- Corpus spongiosum
- Smenial vesicals
- Corpora cavernosum
- Corpus spongiosum
- Corpora cavernosum
- Corpus spongiosum
- Bulb of penis

21. PHYSIOLOGY
OF
ERECTION

22. 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.

23. 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.

24. 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

26. 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

27. MOLECULAR MECHANISM OF CONTRACTION
CYTOSOLIC INFLUX –
Ca++
Calmodulin-4 Ca++
binds
to myosin kinase
Inhibit myosin actin
interaction
Smooth muscle
contraction

28. 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

29. MOLECULAR MECHANISM
Ca ++ Falls
Ca++
dissociates from
calmodulin
Dissociates
from Myosin
kinase
Relaxes muscle

30. SMOOTH MUSCLE CONTRACTION

31. 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.

32. 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

33. PHASES OF ERECTION
• Flaccid phase
• Latent or filling phase
• Tumescent phase
• Full erection phase
• Skeletal or rigid erection phase
• Detumescent phase

34. 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.

35. 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

36. THANK YOU