The Endocrine System

Nursing Department

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At the end of this lecture, you will be able to:

Distinguish between exocrine and endocrine glands.

Describe the locations and function of :

hypothalamus and pituitary gland, thyroid gland, parathyroid

glands, adrenal glands, pancreatic islets.

Describe the location, hormones, and functions of the male and female

gonads, pineal gland and role of the thymus in immunity.

OBJECTIVES

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INTRODUCTION

The body contains two kinds of glands:

1. Exocrine glands:

include sudoriferous(sweat), sebaceous (oil), mucous, and digestive

glands.

2. Endocrine glands:

include the pituitary, thyroid, parathyroid, adrenal, and pineal glands.

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In addition, several organs and tissues are not exclusively classified as

endocrine glands but contain cells that secrete hormones.

These include the hypothalamus, thymus, pancreas, ovaries, testes,

kidneys, stomach, liver, small intestine, skin, heart, adipose tissue, and

placenta.

Cont.

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For many years, the pituitary gland or hypophysis was called the “master”

endocrine gland because it secretes several hormones that control other

endocrine glands.

We now know that the pituitary gland itself has a master.

Hypothalamus and Pituitary Gland

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• The pituitary gland is a pea-shaped structure that measures 1–1.5 cm (0.5

in.) in diameter and lies in the hypophyseal fossa of the sella turcica of the

sphenoid bone.

• It attaches to the hypothalamus by a stalk.

Cont.

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And has two anatomically and functionally separate portions:

The anterior pituitary

the posterior pituitary.

The anterior pituitary (anterior lobe), also called the adenohypophysis

(adeno- = gland; -hypophysis = undergrowth), accounts for about 75% of

the total weight of the gland and is composed of epithelial tissue.

Cont.

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The anterior pituitary consists of two parts in an adult: The pars distalis is

the larger portion, and the pars tuberalis.

The anterior pituitary secretes hormones that regulate a wide range of

bodily activities, from growth to reproduction.

Five types of anterior pituitary cells:

1. Somatotrophs.

2. Thyrotrophs.

3. Gonadotrophs.

4. Lactotrophs.

5. Corticotrophs.

Cont.

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The posterior pituitary (posterior lobe), also called the

neurohypophysis (neuro- = nerve), is composed of neural tissue.

It also consists of two parts: the pars nervosa and the pars

intermedia.

cont.

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Thyroid Gland

The butterfly-shaped thyroid gland is located just inferior to the

larynx (voice box).

It is composed of right and left lateral lobes, one on either side of

the trachea that are connected by an isthmus(IS-mus = a narrow

passage) anterior to the trachea.

About 50% of thyroid glands have a small third lobe, called the

pyramidal lobe.

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It extends superiorly from the isthmus.

The normal mass of the thyroid is about 30 g (1 oz).

two hormones secreted from thyroid: thyroxine which is also

called tetraiodothyronine (T4)and triiodothyronine (T3)

cont.

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Partially embedded in the posterior surface of the lateral lobes of the

thyroid gland are several small, round masses of tissue called the

parathyroid glands (para- = beside). Each has a mass of about 40

mg (0.04 g).

Usually, one superior and one inferior parathyroid gland are attached

to each lateral thyroid lobe, for a total of four.

Parathyroid Glands

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Parathyroid hormone is the major regulator of the levels of:

Calcium(Ca2+)

Magnesium (Mg2+)

Phosphate (HPO42−)

Ions

In the blood.

Cont.

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Adrenal Glands

The paired adrenal glands or suprarenal glands, one of which lies

superior to each kidney in the retroperitoneal space, have a flattened

pyramidal shape.

In an adult, each adrenal gland is 3–5 cm in height, 2–3 cm in width, and

a little less than 1 cm thick, with a mass of 3.5–5 g, only half its size at

birth.

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The adrenal glands differentiate into two structurally and functionally

distinct regions:

Adrenal cortex: Is subdivided into three zones, each of which

secretes different hormones.

Adrenal medulla: The inner region of the adrenal gland, the

adrenal medulla, is a modified sympathetic ganglion of the

autonomic nervous system (ANS).

The two major hormones synthesized by the adrenal medulla are

epinephrine (ep′-i-NEF-rin) and norepinephrine.

cont.

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The pancreas (pan- = all; -creas = flesh) is both an endocrine gland

and an exocrine gland.

A flattened organ that measures about 12.5–15 cm (5–6 in.) in length,

the pancreas is located in the curve of the duodenum, the first part of

the small intestine, and consists of a head, a body, and a tail.

Roughly 99% of the exocrine cells of the pancreas are arranged in

clusters called acini.

Pancreatic Islets

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Each pancreatic islet includes four types of hormone-secreting cells:

1. Alpha or A cells constitute about 17% of pancreatic islet cells and

secrete glucagon.

2. Beta or B cells constitute about 70% of pancreatic islet cells and

secrete insulin.

3. Delta or D cells constitute about 7% of pancreatic islet cells and

secrete somatostatin.

4. F cells constitute the remainder of pancreatic islet cells and secrete

pancreatic polypeptide.

Cell Types in the Pancreatic Islets

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Ovaries and Testes

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Gonads are the organs that produce gametes—sperm in males and

oocytes in females. In addition to their reproductive function, the

gonads secrete hormones.

The ovaries, paired oval bodies located in the female pelvic cavity,

produce several steroid hormones, including two estrogens and

progesterone.

The male gonads, the testes, are oval glands that lie in the

scrotum.

The main hormone produced and secreted by the testes is

testosterone, an androgen or male sex hormone.

Cont.

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Pineal Gland and Thymus

The pineal gland (PI-N-ē-al = pinecone shape) is a small endocrine gland

attached to the roof of the third ventricle of the brain at the midline.

The pineal gland secretes melatonin.

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1-The endocrine glands consist of -------

A. Sebaceous (oil).

B. Pituitary, thyroid.

C. Sweat gland.

D. Mucous.

2- Thyroid gland is located--------

A. Just inferior to the larynx.

B. Just posterior to the larynx.

C. Just superior to the larynx.

D. Just anterior to the larynx.

3- the pancreatic gland is located in ---------

A. The curve of the large intestine.

B. The curve of the duodenum.

C. The curve of the jejunum.

D. The curve of the liver.

4- The ovaries, paired oval bodies located

in the ---------

A. Abdominal cavity.

B. Renal cavity .

C. Male pelvic cavity .

D. Female pelvic cavity .

System ReviewChoose Correct answer?

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