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1

Location of Major Endocrine Organs

Major endocrine glands:
-Pituitary
-Pineal
-Thyroid/Parathyroid
-Adrenal

Organs containing endocrine cells: hypothalamus, skin,Thymus, Heart, liver, stomach, Small intestine, pancreas, kidney, ovary, testes, adipocytes

2

- Second messenger system of the body
- Uses chemical messages (hormones) that are released into the blood
- Hormones control several major processes
*Reproduction
*Growth and development
*Mobilization of body defenses
*Maintenance of much of homeostasis
*Regulation of metabolism

Endocrine System

3

- are produced by specialized cells
- Cells secrete __ into extracellular fluids
- Blood transfers __ to target sites
- regulate the activity of other cells

Hormones

4

4 Main Groups of Chemicals that Act as Hormone

1. Protein/Glycoprotein - insulin, growth hormone, PTH
2. Small Peptide Molecules - Vasopressin and products of enteroendocrine cells
3. Amino Acid Derivatives - thyroxine, epinephrine and norepinephrine
4. Steroid - derived from cholesterol like adrenal cortical hormone, ovarian and testicular hormones

5

Control of Hormone Release

- Hormone levels in the blood are maintained by negative feedback
- A stimulus or low hormone levels in the blood triggers the release of more hormone
- Hormone release stops once an appropriate level in the blood is reached

6

Endocrine glands are activated by other hormones

Hormonal Stimuli of Endocrine Glands

7

Changing blood levels of certain ions stimulate hormone release

Humoral Stimuli of Endocrine Glands

8

- Nerve impulses stimulate hormone release
- Most are under control of the sympathetic nervous system

Neural Stimuli of Endocrine Glands

9

Characteristics of Endocrine Glands

1. The glands are ductless; thus, hormonal secretions are poured directly to the blood through the capillaries.

2. The internal supporting framework is reticular tissue.

3. Highly vascular, thus provided with rich capillary networks among and between groups of secretory cells.

4. The capillaries are fenestrated type in which endothelial wall contains numerous pores or openings which are covered by very thin diaphragms.

10

Development of the Endocrine System

On the basis of their germ layer of origin, the endocrine glands may either be ectodermal, mesodermal or endodermal.

1. Ectodermal in origin - Pituitary gland; Pineal gland; Adrenal medulla

2. Mesodermal in origin - Adrenal cortex; Leydig cells of the testis; Theca interna cells of the ovary

3. Endodermal in origin - Thyroid gland; Parathyroid gland; Islets of Langerhans; Parafollicular cells or C-cells

11

Development of the Pituitary Gland

This develops from two sources:
1. Rathke’s pouch
- Ectodermal outpocketing of the stomodeum (future mouth)
- Gives rise to the ADENOHYPOPHYSIS

2. Infundibulum
- Downward extension of the diencephalon
- Gives rise to the NEUROHYPOPHYSIS

12

- Anterior wall of Rathke’s pouch gives rise to the Pars distalis and the Pars tubercles
- Posterior wall of Rathke’s pouch gives rise to the Pars intermedia

ADENOHYPOPHYSIS

13

- Pars nervosa (infundibular process)
- Infundibular stem (stalk)
- Median eminence of tuber cinereum

NEUROHYPOPHYSIS

14

- Also known as the hypophysis cerebri.
- The hypophysis is a pea-sized glandular organ lodged in the hypophyseal fossa of the sella tursica of the body of the sphenoid.
- It is connected by the infundibulum stalk to the base of the brain and is covered by a capsule of dense connective tissue.

PITUITARY GLAND

15

Divisions of the Hypophysis

1. Adenohypophysis
- Anterior part derived from the Rathke’s pouch
- An outgrowth from the ectodermal roof of the primitive oral cavity

2. Neurohypophysis
- Posterior part developed as a downgrowth from the floor of the diencephalon

16

- Also known as the anterior pituitary
- Subdivisions:
*Pars distalis
*Pars intermedia
*Pars tuberalis

Adenohypophysis

17

- Largest subdivision of the adenohyphysis.
- The cells are grouped into 2 categories:
1. Chromophils
2. Chromophobes

PARS DISTALIS

18

Chromophils

2 types of cells based on affinity to stains
1. Acidophils – secrete prolactin and growth hormone
2. Basophils - secrete FSH, LH, TSH, ACTH

19

- Smallest and least numerous among the cells in the pars distills
- Since they are small, their nuclei lie close to each other; and their cytoplasm is scanty, thus hardly seen.
- These cells are referred to as reserve cells since some of them may differentiate into acidophils or basophils as the need arises

Chromophobes

20

Stimulates release of Thyrotropin (TSH)

Thyrotropin releasing hormone (TRH)

21

Stimulates release of FSH and LH

Gonadotropin releasing hormone (GnRH)

22

Inhibits release of both GH and TSH

Somatostatin

23

Stimulates release of GH

Growth hormone-releasing hormone (GHRH)

24

Inhibits release of Prolactin

Dopamine

25

Stimulates synthesis of pro-opiomelanocortin (POMC) and release of both B-lipotropin and ACTH

Corticotropin-releasing hormone

26

% Total cells: 50
Hormone produced: SOMATOTROPIN (GROWTH HORMONE)
Major Function: Stimulates growth in epiphyseal plates of long bones via insulin-like growth factors (IGF) produced in liver

Somatotrophs

27

% Total cells: 15-20
Hormone Produced: PROLACTIN (PRL)
Major function: Promotes milk secretion

Lactotrophs or Mammotrophs

28

% Total cells: 10
Hormone Produced: FSH, LH, ICSH (Interstitial cell-stimulating Hormone)
Major Function: FSH promotes ovarian follicle devt and Estrogen secretion in women and spermatogenesis in men: LH promotes ovarian follicle maturation and Progesterone secretion in women and interstitial cell androgen secretion in men

Gonadotrophs

29

% Total cells: 5
Hormone Produced: THYROTROPIN (TSH)
Major Function: Stimulate TH synthesis, storage and liberation

Thyrotrophs

30

% Total cells: 15-20
Hormone Produced and Functions:
*ADRENAL CORTICOTROPIN (ACTH) - Stimulates secretion of adrenal cortex hormones

*LIPOTROPIN (LPH) - Helps regulate lipid metabolism

Corticotrophs