Viscera and Visceral Systems

Question 1

Viscera

Answer 1

-Organs that regulate internal environment
-Occupy cavities in the body: thorax, abdomen, pelvis (also found in head and neck)
-Involved with secretion, excretion, digestion, absorption (hollow or solid)

Question 2

Hollow Viscera

Answer 2

-typically tubular, with a cylindrical wall and a lumen
Lumen- ‘light’
Mucosa- (internal layer) may have folds that increase surface area for absorption
Muscularis- (middle layer) contains smooth muscle that may produce waves of contraction- ‘peristalsis’
Serosa- (external layer) minimises friction/ usually derived from lining of body cavities/ can be continuous with a mesentery attaching viscera to body wall

Question 3

Muscle Coats

Answer 3

-Circular and longitudinal smooth muscle
-Provides motility and expansion e.g- bladder/ rectum
*At critical point of storage (stretch) reflexes are initiated to cause micturition or defecation

Question 4

Lumen of tubular viscus

Answer 4

-May have dilatations or constrictions
-Constrictions (usually at beginning or end)
 a duct tends to narrow where it approaches the wall of a hollow viscus (orifice)
calculus (stone) likely to lodge at orifice

Question 5

Sphincter

Answer 5

(1) Anatomical sphincter
Localised muscle thickening around wall of tubular viscus- controls passage and prevents reflux of contents
Also at distal ends of ducts, near an external orifice
(2) Functional sphincter
No localised muscular thickening

Question 6

Involuntary vs. Voluntary Sphincters

Answer 6

1. Involuntary
   Made up of smooth muscle supplied by the ANS/ 1st line of defence
2. Voluntary
   Made of skeletal muscle supplied by the somatic nervous system/ 2nd line of defence

Question 7

Solid Viscus

Answer 7

-Glands- clusters for secretory cells
-External capsule (protection) and serosa (reduces friction)
-May have subdivisions (outer cortex and inner medulla)/ be organised into lobes
N.B- Structures adjacent to solid viscera produce grooves and impressions on it e.g- heart

Question 8

Exocrine Glands

Answer 8

-Glands that secrete into a duct or system of ducts
-ducts emerge from hilum of viscera
-open into hollow viscera
e.g- liver and bile duct

Question 9

Endocrine glands

Answer 9

-Glands that secrete directly into bloodstream
-Usually secrete hormones that act in other parts of the body
-Rich blood supply
e.g- adrenal glands
N.B- Some glands are both e.g- pancreas

Question 10

Serous membranes

Answer 10

-Single membrane that lines a body cavity and contains a space within it e.g- pleura & pericardium in thoracic cavity
-Produces fluid that lubricates the cavity/ lines body wall
-Parietal layer= lines body wall and receives nerve and blood supply from body wall (somatic_
-Visceral layer= covers viscera and receives same nerve and blood supply of viscera (autonomic)

Question 11

Peritoneal Cavity

Answer 11

-Closed cavity in the abdomen lined by a serous membrane called the peritoneum
-Some viscera are suspended in body cavity by a mesentery- connects viscera to body wall and conveys vessels and nerves

Question 12

Role of Mesentery

Answer 12

1. Pathway for nerves and vessels
2. Mobility

Question 13

Paired viscera

Answer 13

-Each develop and are located on one side of the body e.g- ureters, kidneys, male reproductive viscera
-Same nerve and blood supply from same side

Question 14

Referred pain

Answer 14

-perception of pain in areas other than the site of stimulation
-due to convergence of two inputs to the same population of neurons at a given spinal segmental level
N.B- pain from a paired viscus is referred to skin on same side (ipsilateral

Question 15

Unpaired viscera

Answer 15

-GI tract + associated glands and ducts
-Unpaired viscera receive a bilateral nerve supply
-Visceral pain referred to midline skin because sensory impulses arrive in
Both left and right sides of spinal cord segments simultaneously
N.B- pain is initially felt in midline  referred to local overlying skin when somatic nerves involved