Lecture 6 – The Endocrine System

Question 1

Endocrine 2

Answer 1

o Ductless glands

o Secrete directly into the blood stream

Question 2

Exocrine 3

Answer 2

o Glands with ducts
o Secrete directly into or onto an organ or tissue. Secrete pancreatic digestive enzymes via the pancreatic duct at the hepatopancreatic ampulla, along with bile from the gall bladder
o E.g. Salivary glands, sweat glands, pancreas (digestive juices)

Question 3

Components of the endocrine system 8

Answer 3

•	Pituitary 
•	Thyroid
•	Parathyroids
•	Pancreas
•	Suprarenals (adrenals)
•	Gonads - Ovaries and testes
•	Thymus gland
Pineal gland

Question 4

Thymus gland 3

Answer 4

Thymus:
• Stimulates maturation of T lymphocytes.
• Consists of two lobes situated in the upper part of the chest behind the sternum.
• It enlarges during childhood, and atrophies after puberty.

Question 5

Pineal gland 4

Answer 5

• Secretes melatonin which maintains the “biological clock”.
• Large in childhood but shrinks at puberty.
• Believed to play a role in sexual development, seasonal breeding, hibernation in animals.
• Pineal tumours have been linked to precocious puberty (when a child’s body begins changing into that of an adult (puberty) too soon).

Anterior triangle	Posterior triangle
Anterior border of scm/midline/ inferior border of mandible.
Strap muscles
Hyoid
Submandibular salivary gland
Larynx/ trachea
Carotid artery
Internal jugular vein
	Posterior triangle - Posterior border of scm/ anterior border of trapezius/ superior border of clavicle
Scalenus anterior
Phrenic nerve
Subclavian artery/vein
Brachial plexus
Scalenus medius
Accessory nerve

Question 6

Anterior triangle 7

Answer 6

1. Anterior border of scm/midline/ inferior border of mandible.
2. Strap muscles
3. Hyoid
4. Submandibular salivary gland
5. Larynx/ trachea
6. Carotid artery
7. Internal jugular vein

Question 7

Posterior triangle 7

Answer 7

1. Posterior triangle - Posterior border of scm/ anterior border of trapezius/ superior border of clavicle
2. Scalenus anterior
3. Phrenic nerve
4. Subclavian artery/vein
5. Brachial plexus
6. Scalenus medius
7. Accessory nerve

Question 8

Pituitary gland 5

Answer 8

• Pituitary is attached to the under surface of the brain (hypothalamus) by the infundibulum, or pituitary stalk and located in the sella turcica of the sphenoid bone.
• Secretions of the pituitary include Hgh.
• Hypopituitarism - diminished hormone secretion by the pituitary gland, causing dwarfism in children and premature ageing in adults. 45.5 people out of 100,000. Most (61%) due to tumours.
• Hyperpituitarism – gigantism. A condition due to the primary hypersecretion of pituitary hormones; it typically results from a pituitary adenoma.

Question 9

Thyroid gland 4

Answer 9

• Positioned on the trachea, anterolateral to the trachea and larynx.
• Overlies the 2nd and 3rd tracheal rings anteriorly.
• Laterally related to cricoid and laryngeal cartilages.
• Extends from vertebral levels C5 – T1.

Question 10

Thyroid gland- structure 6

Answer 10

• Consists of left and right lobes united by a relatively narrow isthmus.
• A pyramidal lobe is present in approximately 50% of the population, usually on the left side.
• The thyroid gland is covered by the infra-hyoid (below hyoid) strap muscles:
1. Omohyoid (lateral)
2. Sternohyoid (medial)
3. Sternothyroid (deep)

Question 11

Thyroid dissection 5

Answer 11

• Anterior jugular
• Internal jugular
• Carotid arteries
• Submandibular gland
• Strap muscles

Question 12

Parathyroid glands 5

Answer 12

• Two pairs embedded in the deep surface of the thyroid gland.
• Usually supplied by the inferior thyroid arteries.
• Produce parathyroid hormone.
• Regulate the body’s calcium levels.
• NOTE sup. thyroid arteries and external laryngeal nerve; inferior thyroid arteries, recurrent laryngeal nerves.

Question 13

Arterial supply of the thyroid gland 6

Answer 13

External common carotid artery
Internal common carotid artery
Superior thyroid artery
Inferior thyroid artery
Subclavian artery
Thyrocervical trunk

Question 14

Venous drainage of the thyroid gland 6

Answer 14

Internal jugular vein
Brachiocephalic vein
Superior Vena Cava
Superior/Middle/Inferior thyroid veins

Question 15

What is the consequence of injury to the recurrent laryngeal nerve during thyroid surgery?

Answer 15

Vocal cord paresis or paralysis due to iatrogenic injury of the recurrent laryngeal nerve (RLNI) is one of the main problems in thyroid surgery.

Question 16

What does the accessory nerve supply?

Answer 16

The spinal accessory nerve innervates two muscles – the sternocleidomastoid and trapezius.

Question 17

Suprarenal (adrenal) glands 3

Answer 17

• Located on the superior poles of the kidneys;
• Each adrenal gland is supplied by a superior and middle adrenal artery arising directly from the aorta and/or the inferior phrenic arteries, and an inferior adrenal artery which arises from the renal artery.
• Venous drainage is by a single adrenal vein on each side. Right adrenal vein  IVC. Left adrenal vein  Renal vein  IVC.

Question 18

Kidneys 3

Answer 18

• The kidneys are retroperitoneal organs which lie in the paravertebral gutters between the levels of the twelfth thoracic (T12) and third lumbar (L3) vertebrae. The hilum of the kidney lies at approximately the L1 level. This is the transpyloric plane, which passes through several important structures.

Ureter leaves kidney at the hilum and terminate at the urinary bladder.

Question 19

Why do the kidneys lie at slightly different levels of the posterior abdominal wall?

Answer 19

The left kidney is located slightly more superior than the right kidney due to the larger size of the liver on the right side of the body.

Question 20

Pancreas 6

Answer 20

• Described as having a head, neck, body (crosses abdominal aorta) and tail; uncinate process. It has a lobulated, typically glandular appearance.
• A mixed exo- and endocrine gland. Insulin produced in the islets of Langerhans.
• Located on the posterior abdominal wall.
• Head is enclosed by the loop of the duodenum “C- shape”, it wraps around a large vascular bundle, and projects inferiorly as the uncinate (“hook-like”) process.
• Tail is located in the hilum of the spleen.
• Lies across the posterior part of the abdomen at the level of L1 and L2.

Question 21

Blood supply of the pancreas 2

Answer 21

• From the coeliac trunk (via the splenic and gastroduodenal arteries) and the superior mesenteric artery.
• Venous drainage to the liver via the hepatic portal vein.

Question 22

What are the main branches of the coeliac trunk?

Answer 22

3 main divisions:
Left gastric artery
Common hepatic artery
Splenic artery.
•	The splenic artery can be identified by its typical tortuous appearance. Follow this artery to the left along the superior border of the body and tail of the pancreas, which it supplies with blood.

Question 23

What can a splenomegaly be caused by?

Answer 23

An enlarged spleen can be caused by infections, cirrhosis and other liver diseases, blood diseases characterised by abnormal blood cells, problems with the lymph system, or other conditions.

Question 24

Ovaries 7

Answer 24

1. The ovaries suspended from the posterior of the broad ligament by the mesovarium.
2. Blood supply is from the ovarian arteries, which originate from the abdominal aorta, around L3. The artery runs in the suspensory ligament of the ovary, from the lateral wall of the pelvis towards the ovary.
3. Venous drainage via the ovarian veins, which terminate in the IVC (right side) and renal vein  IVC (left side).
4. The ovaries lie in the superior part of the pelvic cavity, on each side of the uterus.
5. Identify the fimbriae of the uterine tubes lying lateral to the ovaries. Follow the uterine tubes (infundibulum, ampulla, and isthmus) toward the uterus.
6. The normal orientation of the uterus is anteverted and anteflexed, with the fundus lying on the superior surface of the urinary bladder.
7. The pelvic organs are covered by a serous membrane, the peritoneum, which forms the broad ligament of the uterus. This forms recesses between the uterus and the bladder (the vesicouterine pouch), and the uterus and the rectum (the rectouterine pouch, or pouch of Douglas), where pus can accumulate during an infection.

Question 25

Testes 10

Answer 25

• Produce testosterone
• Suspended in the scrotum by the spermatic cord.
• The spermatic cord consists of the ductus deferens, testicular artery, testicular veins plus other structures.
• The veins terminate in the IVC (right side) and the renal vein (left side).
• The testicular veins form the pampiniform plexus around the outside of the spermatic cord to cool incoming arterial blood. The drainage of the two sides is different. High pressure sometimes develops in the left testicular vein, leading to a varicocoele (varicose veins in the pampiniform plexus), said to resemble a “bag of worms” on palpation.
• The testes develop inside the abdomen, then descend through the inguinal canal to reach the scrotum (usually at birth or soon after). During their descent, the testes become covered by the three layers of the anterolateral abdominal wall. These layers form the three layers of the spermatic fascia, external, internal, and cremasteric (middle).
• The testes are suspended outside the body, in order to keep the temperature below the body’s core temperature. The position of the testes can be altered depending on the external temperature.
• The wall of the scrotum contains the dartos muscle.
• On the scrotum there is no subcutaneous fat. The skin of the scrotum is lined by the dartos muscle, a layer of smooth muscle that contracts or relaxes depending on the external temperature. It is the dartos that is responsible for the wrinkled appearance of the scrotum.
• Follow the vas deferens from the epididymis on the posterior of the testis to its termination posterior to the bladder. It enters the inguinal canal at the superficial inguinal ring, traverses the inguinal canal, then enters the body cavity via the deep inguinal ring. Because it is a site of potential weakness in the abdominal wall, the inguinal canal is a common site for hernias to develop.