Lecture 41 - Principles of viscera

Question 1

What are the two types of viscera?

Answer 1

Hollow/tubular and solid viscera

Question 2

What are the 4 activities in which viscera are involved?

Answer 2

SEDA - secretion, excretion, digestion, absorption

Question 3

What is the role of all viscera?

Answer 3

To regulate the body’s internal environment.

Question 4

Most organ systems do not include which anatomical region?

Answer 4

The back.

Question 5

What is the inside of a hollow viscera called?

Answer 5

The lumen

Question 6

What are the three layers of hollow viscera?

Answer 6

External - serosa.
Intermediate - muscularis.
Internal - mucosa.

Question 7

What two structural features increase the internal surface area of hollow viscera?

Answer 7

Folds in the mucosa and/or villi on mucosa

Question 8

Where are hollow viscera most likely to have constrictions?

Answer 8

At the beginning and end of the tube.

Question 9

Other than functional and anatomical sphincters, what might cause constrictions in hollow viscera?

Answer 9

Constrictions can be caused by adjacent structures. Eg, the aortic arch compressing the esophagus or the pelvic brim constricting the ureters.

Question 10

Why is it clinically important to know where constrictions are in hollow viscera?

Answer 10

Constrictions are the most likely place that objects will become lodged in hollow viscera, eg calculuses passing from the kidney to the bladder are most likely lodged in an orifice or at the pelvic brim.

Question 11

If you were a doctor, how could you detect an obstruction in a patient’s ureter?

Answer 11

Ingestion of a radioactive dye that is passed in the urine. Upon x-ray the lye will stop or thin out at any restrictions in the ureters.

Question 12

What two subtypes of smooth muscle make up the walls of hollow viscera?

Answer 12

Circular and longitunidal

Question 13

What are the 3 benefits of having smooth muscle in the walls of hollow viscera? Give a specific example of each benefit.

Answer 13

It allows for…

1. Expansion to store large quantities (eg, bladder);
2. Motility (eg, peristalsis of the small intestines)
3. Smooth muscle can be stretched without loosing tension, thus it can contract with enough force to push contents to the exterior (eg, during urination.)

Question 14

Solid viscera are organized into clusters of cells. What are the two way in which hollow viscera may be structurally organized? Give an example of each.

Answer 14

Into either…

1. Cortex (outer) and medulla (inner) (eg, kidneys);
2. Lobes and lobules (eg, lungs)

Question 15

Are lobes of solid viscera divided functionally or structurally?

Answer 15

Trick question: lobes of solid viscera can be divided functionally or structurally.

Question 16

Solid viscera have an external capsule, the ‘serosa.’ What is its role?

Answer 16

Reduce friction.

Question 17

How do adjacent structures affect solid viscera? Give an example.

Answer 17

Solid viscera tend to have impressions/marks from adjacent structures. Eg, left lung has the cardiac impression: the heart and the aortic arch.

Question 18

What are the two types of sphincters of tubular viscera?

Answer 18

Anatomical and functional

Question 19

What are the two main roles of sphincters?

Answer 19

Control passage of contents into the next section and to stop reflux of contents.

Question 20

Describe the structure of an anatomical sphincter. How does this structure control the passage of contents?

Answer 20

Ring of muscle. When the muscle is contracted it ‘strangles’ the tube closed.

Question 21

What happens if you change the tone of a smooth muscle? Give an example.

Answer 21

Anything that alters tension/tone of smooth muscle can cause unchecked flow of contents. Eg, caused by cancer or nerve damage or drugs.

Question 22

Describe the structure of an fuctional sphincter using an example from the lecture. How does this structure control reflux of contents back into the tube?

Answer 22

The ureter enters the muscular wall of the bladder obliquely. Thus, when the bladder contracts during urination it also closes the end of the ureter, and therefore stops reflux. (See slide 12 for illustration.)

Question 23

What is the key difference between anatomical and functional sphincters?

Answer 23

Functional sphincters have no localized muscle thickening.

Question 24

True or false: anatomical sphincters are only ever made of smooth muscle.

Answer 24

False: Anatomical sphincters may have both rings of skeletal muscle and rings of smooth muscle.

Question 25

Give an example of an anatomical sphincter that has a ring of skeletal muscle. Why would an anatomical sphincter have skeletal muscle?

Answer 25

Urethra or rectum. Skeletal muscle gives us voluntary control over the passage of contents out of those tubes and so it acts as a “2nd line of defense” for control of excretion/defecation.

Question 26

What is the serous membrane?

Answer 26

A thin, smooth membrane of cells that secrete serous fluid and surround the cavities of the abdomen and thorax.

Question 27

What are the two structural subdivisions of the serous membrane?

Answer 27

Peritoenum (covers the walls of the body cavity) and visceral (covers the viscera)

Question 28

What are the two structural subdivisions of the visceral serous membrane?

Answer 28

Parietal - abdominal cavity

Pleural - Thoracic cavity

Question 29

With what structure does the parietal serous membrane share its nerve and blood supply?

Answer 29

It shares the nerve and blood supply of the thoracic/abdominal walls.

Question 30

With what structure does the visceral serous membrane share its nerve and blood supply?

Answer 30

It shares the nerve and blood supply of the viscera that it surrounds.

Question 31

Are the parietal and visceral layers of serous membrane structurally separate?

Answer 31

No; they are a single continuous membrane.

Question 32

How does the serous membrane assist the nerves and vessels of the viscera?

Answer 32

The serous membrane wraps around to form a pathway for nerves, arteries, and veins to move from posterior wall of the cavity to the viscera.

Question 33

What is a mesentery?

Answer 33

Fold of peritoneum that suspends viscera in the body cavity.

Question 34

What are the two roles of mesentery?

Answer 34

1. Provide a pathway for nerves and vessels to the viscera.

2. Provide viscera with mobility within the body cavity (eg, for stomach expansion.)

Question 35

Viscera suspended in mesentery are at risk of what injury? What is the most serious consequence of this injury? Give an example of a viscera that is at risk.

Answer 35

Structures within the mesentery are in danger of torsion/twisting. Torsion may block blood supply and cause avascular necrosis. An example of this if twisting of the testes.

Question 36

What is referred pain?

Answer 36

Pain experienced at a site different from its source, usually referred to the skin.

Question 37

What developmental reasons cause referral of pain?

Answer 37

Referred pain arises because somatic structures and visceral structures share the same spinal cord segment but they migrate away from each other during development .

Question 38

Give an example of referred pain.

Answer 38

During a heart attack the sufferer may feel pain in the dermatome of their left upper arm.

Question 39

Give an example of paired viscera. Do a set of paired viscera share the same blood supply?

Answer 39

Kidneys, adrenals, testes, lungs. Each of a set of paired viscera have separate blood supply.

Question 40

True or false: referred pain from paired viscera occurs on both sides of the body because they share the same nerve supply, despite sharing the same blood supply.

Answer 40

False; referred pain from paired viscera occurs on the side of the body that is injured because each of a set of paired viscera has its own distinct nerve supply.

Question 41

True or false: unpaired viscera develop along the midline.

Answer 41

True

Question 42

Where do unpaired viscera refer pain to? Can this change? Why?

Answer 42

The midline, even if the pathology is not at midline. Yes, pain may only shift if the overlying peritoneum is affected by the inflammation. The overlying peritoneum shares the same nerve supply as the overlying skin.

Question 43

From which side of the spinal cord do unpaired viscera receive their nerve supply?

Answer 43

Trick question: unpaired viscera receive their nerve supply from both sides