Lecture 17: The Endocrine And Lymphatic System

Question 1

What are the 2 main classes of hormones?

Answer 1

1. Amino-acid based hormones eg amines, thyroxine, peptides, proteins
2. Steroids
   - synthesised from cholesterol
   - gonadal and adrenocortical hormones

Target cells must have specific receptors to which the hormones bind

Question 2

The pituitary gland and hypothalamus

What are the 2 major lobes of the pituitary?

Answer 2

Pituitary gland has 2 major lobes:

1. Posterior pituitary (lobe):
   - nerve fibres
2. Anterior pituitary (lobe):
   - glandular tissue

Question 3

Hormonal stimuli

Hormones can stimulate other endocrine organs to release their hormones. Give example

Answer 3

Hypothalmic hormones stimulate the release of most anterior pituitary hormones
Anterior pituitary hormones stimulate targets to secrete more hormones from target endocrine organs

Question 4

What is the relationship between the posterior pituitary and the hypothalamus?

Answer 4

1) hypothalmic neurons synthesize oxytocin and ADH
2) oxytocin and ADH are transported along the hypothalmic-hypophyseal tract to the posterior pituitary
3) oxytocin and ADH are stored in axon terminals in the posterior pituitary
4) oxytocin and ADH are released into the blood when hypothalmic neurons fire

Question 5

Pituitary-hypothalmic relationships

Ie between postior lobe and anterior lobe

Answer 5

Posterior lobe:

• extension of hypothalmic neural tissue
• nuclei of the hypothalamus synthesize the neurohormones oxytocin and ADH
• neurohormones are transported r the posterior pituitary

Anterior lobe:

• it is glandular
• hypophyseal portal system
• carries releasing and inhibiting hormones

Question 6

Relationship between the anterior pituitary and the hypothalamus

Answer 6

1) When appropriately stimulated, hypothalmic neurons secrete releasing and inhibiting hormones into the primary capillary plexus.
2) hypothalmic hormones travel through the portal veins to the anterior pituitary where they stimulate or inhibit release if hormones from anterior pituitary.
3) anterior pituitary hormones are secreted into the secondary capillary plexus

Question 7

List the anterior pituitary hormones

Go Ahead Fuck The Pregnant Lady

Answer 7

Growth hormone
Thyroid-stimulating hormone
Adrencorticotropic hormone
Follicle stimulating hormones
Luteinizing hormone
Prolactin 

All are proteins
TSH, ACTH, FSH, LH are all tropic hormones (regulate secretory action of other endocrine glands)

Question 8

What is the function of the growth hormone?

What happens if it hyper secretes or hyposecretes

Answer 8

-Stimulates most cells, but targets bone and skeletal muscle
-promotes protein synthesis and encourages use of fats for fuel
The direct action of GH is to stimulate liver, skeletal muscles bone, and cartilage to produce insulin-like growth factors

Hypersecretion: 
-in children results in gigantism 
-in adults results in acromegaly 
Hyposecretion:
-in children results in pituitary dwarfism

Question 9

What is the function of thyroid-stimulating hormone

How is it regulated

Answer 9

Stimulates the normal development and secretory activity of the thyroid
Regulation of TSH
-inhibited by rising blood levels of thyroid hormones that act on the pituitary and hypothalamus

Question 10

What is the function of adrenocorticotropic hormone

Function of prolactin

Answer 10

Adrenocorticotropic hormone:
-stimulates the adrenal cortex to release corticosteroids

Prolactin:

• stimulates milk production
• blood levels rise towards end of pregnancy
• suckling stimulates PRL release and promotes continues milk production

Question 11

Gonadotropins

Answer 11

• Follicle-stimulating hormone (FSH) and luteinizing hormone
• FSH stimulates gamete (egg or sperm) production
• LH promotes production of gonadal hormones

Question 12

What are the 3 parts the lymphatic system consists of?

What are the functions of the lymphatic system?

Answer 12

Parts:

1. A network of lymphatic vessels
2. Lymph (fluid)
3. Lymph nodes

Function:
Returns interstitial fluid and leaked plasma proteins back to the blood
-once interstitial fluid enters lymphatics, it is called lymph
Together with lymphoid organs and tissues, provide the structural basis of the immune system

Question 13

What are the lymphatic vessels in the system?

Answer 13

It’s a one one system, lymph flows towards the heart
Lymph vessels (lymphatics) include:
-lymphatic capillaries (smallest)
-lymphatic collecting vessels (medium sized)
-lymphatic trunk and ducts (largest)

Question 14

Describe the lymphatic capillaries

Answer 14

Similar to blood capillaries except:
-very permeable (take up cell debris, pathogens, and cancer cells)
-endothelial cells overlap to form one-way mini valves, and are anchored by collagen filaments, preventing collapse of capillaries
None in the CNS
Lacteals: specialised lymph capillaries present in intestinal mucosa
-absorb digested fat and deliver fatty lymph (chyle) to the blood

Question 15

Describe the lymphatic collecting vessels

Answer 15

Similar to veins, except
-have thinner walls, with more internal valves
Trunks are formed by the union of the largest collecting ducts
-paired lumbar
-paired subclavian
-paired jugular trunks
-a single intestinal trunk

Question 16

What are lymphatic ducts, what do they do?

Answer 16

Lymph is delivered into one of 2 large ducts
-right lymphatic ducts drains the right upper arm and the right side if the head and thorax
-thoracic duct arises from cisterna chyli and drains the rest of the body
Each empties lymph into venous circulation at the junction of the internal jugular and subclavian veins on its own side of the body
Lymph is propelled by:
-pulsation of nearby arteries
-contraction of smooth muscle in the walls of the lymphatics

Question 17

What are the lymphoid cells of the body?

Answer 17

Aka lymphocytes: warriors of immune system
-macrophages phagocytise foreign substances and help activate T cells
Two main varieties
-T cells
-B cells
T cells and B cells protect against antigens
T cells
-manage the immune response
-attack and destroy foreign cells
B cells
-produce plasma cells, which secrete antibodies

Question 18

What is the function of the lymphoid tissue?

Answer 18

-Houses and provides a proliferation site for lymphocytes
-furnishes a surveillance vantage point
Two main types:
1. Diffuse lymphatic tissue
-diffuse lymphatic tissue comprises scattered reticular tissue elements in every body organ
-larger collections in the lamina propria if mucous membranes and lymphoid organs

2. Lymphatic follicles
   - lymphatic follicles (nodules) are solid, spherical oldies of tightly packed reticular elements

Question 19

What are lymph nodes what is their function?

Answer 19

-principle lymphoid organs of the body
-embedded in connective tissue, in clusters along lymphatic vessels
-near the body surface in inguinal, axillary and cervical regions of the body
Functions:
1-filter lymph-macrophages destroy microorganisms and debris
2- immune system- lymphocytes are activates and mount an attack against antigens

Question 20

Describe the structure of a lymph node

Answer 20

-Bean shaped with an external fibrous capsule
-Two histology ally distinct regions
Cortex- which contains follicles with germinal centres
Medulla- lymph sinuses contain macrophages
T cells circulate continuously among the blood, lymph nodes, and lymphatic stream

Question 21

Circulation of the lymph nodes

Answer 21

Lymph

• enters via afferent lymphatic vessels
• travels through large subscapular sinus and smaller sinuses
• exits the node at the hilum via efferent vessels

Question 22

Spleen

Answer 22

-Largest lymphoid organ
-served by splenic artery and vein
Functions:
-site of lymphocyte proliferation and immune surveillance and response
-cleanses the blood of aged cells and platelets and debris

• stores breakdown products of RBC’s eg iron
• site of fetal erythrocyte production (normally stops after birth)
• has a fibrous capsule and trabeculae
• contains lymphocytes, macrophages, and huge numbers if erythrocytes.

Question 23

Describe the structure of the spleen

Answer 23

Has 2 distinct areas
-White pulp around central arteries
-red pulp in venous sinuses and splenic cords
(Rich in macrophages for disposal of worn-out RBS’s and blood borne pathogens

Question 24

What is the thymus and what is its function?

Answer 24

Size with age:
-In infants, it is found in the inferior neck and extends info the mediastinum, where it is partially overlies the heart
-increase in size and is most active during childhood
-stops growing during adolescence and then gradually atrophies
Contains densely packed lymphocytes and scattered macrophages
Differs from other lymphoid organs in important ways
-it functions strictly in T lymphocyte maturation
-it doesn’t directly fight antigens

Question 25

Tonsils

Answer 25

Simplest lymphoid organs
Form a ring of lymphatic tissue around the pharynx
-palatine tonsils- at posterior end of the oral cavity
-lingual tonsils- grouped at base of tinge and
-pharyngeal tonsils- in posterior wall of the nasopharynx
Epithelial tissue overlying tonsil masses invagination, forming tonsillar crypts
Crypts trap and destroy bacteria and particulate matter

Question 26

Mucosa- associated lymphatic tissue

MALT

Answer 26

-Peyers patches, tonsils, and the appendix (digestive tract)
-Lymphoid nodules in the walls of the bronchi (respiratory tract)
Protects the digestive and respiratory systems from foreign matter
Peyers patches
-in the wall of the distal portion of the small intestine
-similar structures are also found in the appendix
-destroy bacteria, preventing them from breaching the intestinal wall
-generate “memory” lymphocytes

Question 27

Developmental aspects

Answer 27

Lymphatic organs arise from mesoderm (except the thymus: endoderm)
Except for the spleen and tonsils, lymphoid organs are poorly developed at birth.

Question 28

List the endocrine structures of the body

Answer 28

Pineal 
Hypothalamus 
Pituitary gland 
Thyroid gland 
Parathyroid gland 
Thymus 
Adrenal glands 
Pancreas 
Ovary 
Testis