Anatomy of Endocrine Glands

Hafiz Waheed Ullah

B. Sc. Pharm.D, M. Phil, Ph.D* (Pharmacognosy)
Leads College of Pharmacy(LLU)
Outline

Pituitary gland: structure and relation to hypothalamus

Thyroid gland: structure

Adrenal gland: structure

 Endocrinology
• Endocrinology is a branch of biology and medicine focusing on the endocrine system and
its secretion of hormones
• There are 2 types of glands:

Exocrine gland makes substances

Endocrine glands are ductless glands of
such as sweat, tears, saliva, milk, and
the endocrine system that secrete their
digestive juices, and releases them
products, hormones, directly into the
through a duct or opening to a body
blood.
surface.
Examples:
Examples: sweat glands, lacrimal
Pineal gland, pituitary gland, pancreas,
glands, salivary glands, mammary
ovaries, testes, thyroid gland, parathyroid
glands, and digestive glands in the
gland, hypothalamus and adrenal glands.
stomach, pancreas, and intestines.
The Endocrine system

• The endocrine system consists of glands widely

separated from each other with no physical
connections
• They are also referred to as ductless glands because
hormones diffuse directly into the bloodstream.
• Hormones are then carried in the bloodstream to target
tissues and organs that may be quite distant, where
they influence cell growth and metabolism.
 Hormones

Chemical substances secreted by cells into the extracellular fluids

• Regulate the metabolic function of other cells
• Have lag times ranging from seconds to hours
• Tend to have prolonged effects
• Are classified as amino acid-based hormones, or steroids
The major processes controlled and integrated by these are
1. Reproduction; growth and development
2. Mobilization of body defenses
3. Maintenance of electrolyte, water, and nutrient balance of the blood
4. Regulation of cellular metabolism and energy balance.
 Major Endocrine Organs

1. Pituitary (Hypophysis) gland

2. Thyroid gland
3. Parathyroid gland
4. Adrenal or Supra-Renal gland The term hypophysis (from the Greek
5. Pancreas for “lying under”)—another name for
the pituitary—refers to the gland's
6. Gonads
position on the underside of the brain
7. Pineal
8. Thymus
 Pituitary gland
• Pituitary gland
– Two-lobed organ that secretes nine major
hormones
• Size & shape
– Pea or Almond
• Location
– Sella turcica (a depression in sphenoid bone
containing pituitary gland)
– Bony cavity at the base of the brain
• In humans, the pituitary gland has two major lobes
– Posterior Pituitary Lobe
– Anterior Pituitary Lobe
 Lobes of Pituitary gland

• Posterior lobe
– Neurohypophysis (neural tissue)
– Infundibulum (funnel shaped connecting stalk)
– Receives, stores, and releases hormones from
the hypothalamus
• Anterior lobe
– Adenohypophysis made up of glandular
epithelium tissue
– Synthesizes and secretes a number of hormones
 Pituitary gland and hypothalamus

• Hypothalamus is classified as a part of the brain rather than an endocrine gland, it controls
the pituitary gland.
• The pituitary gland and the hypothalamus act as a unit, regulating the activity of most of
the other endocrine glands.
• The pituitary gland lies in the hypophyseal fossa of the sphenoid bone below the
hypothalamus, to which it is attached by a stalk.
• It is the size of a pea, weighs about 500 mg and consists of two main parts that originate
from different types of cells.
• There is a network of nerve fibres between the hypothalamus and the posterior pituitary.
 Pituitary-Hypothalamic Relationships
Posterior Lobe
• The posterior lobe is a down growth of hypothalamic neural tissue
• Connected to hypothalamus
– Nerve bundle
– hypothalamic-hypophyseal tract

• This tract arises from neurons in the supraoptic and paraventricular nuclei of the hypothalamus

• Nuclei of the hypothalamus synthesize two hormones

– ADH (supraoptic)
– Oxytocin (paraventricular)
• These hormones are transported to the posterior pituitary
• Stored hormones are released in general circulation when hypothalamic neurons fire.
 Pituitary-Hypothalamic Relationships

• Anterior Lobe
• It is glandular in nature
• Originates from a superior out pocketing of the oral mucosa
• Formed from epithelial tissue

• No direct neural contact with the hypothalamus

• Vascular connection Exists
• This vascular connection, the hypophyseal portal system, consists of:

– The primary capillary plexus (in infundibulum)

– The hypophyseal portal veins
– The secondary capillary plexus (in anterior lobe)
 Anterior pituitary

• The anterior pituitary is supplied indirectly with arterial blood that has already
passed through a capillary bed in the hypothalamus.
• This network of blood vessels forms part of the pituitary portal system, which
transports blood from the hypothalamus to the anterior pituitary.
• This blood transports releasing and inhibiting hormones secreted by the
hypothalamus
Hormones released by Anterior Pituitary gland

• Growth hormone. regulates growth and physical development. It can stimulate

growth in almost all tissues. Its primary targets are bones and muscles.
• Thyroid-stimulating hormone. activates thyroid to release thyroid hormones
thyroid gland and the hormones it produces are crucial for metabolism.
• Adrenocorticotropic hormone. Stimulates adrenal glands to produce cortisol and
other hormones.
• Follicle-stimulating hormone. involved with estrogen secretion and the growth of
egg cells in women. It’s also important for sperm cell production in men.
 Hormones released by Anterior Pituitary gland

• Luteinizing hormone. involved in the production of estrogen in

women and testosterone in men.
• Prolactin. helps women who are breastfeeding produce milk.
• Endorphins. have pain-relieving properties and are thought to
be connected to the “pleasure centers” of the brain.
• Enkephalins. are closely related to endorphins and have similar
pain-relieving effects.
• Beta-melanocyte-stimulating hormone. This hormone helps to
stimulate increased pigmentation of skin in response to exposure
to ultraviolet radiation
Hormones released by Anterior Pituitary gland
Negative feedback mechanism
 Posterior pituitary
• The posterior pituitary is formed from nervous tissue and consists of nerve cells
• These neurons have their cell bodies in the supraoptic and paraventricular nuclei of the
hypothalamus.
• Their axons form a bundle known as the hypothalamohypophyseal tract.
• Posterior pituitary hormones are synthesised in the nerve cell bodies, transported along the
axons and stored in vesicles within the axon terminals.
• Nerve impulses from the hypothalamus trigger exocytosis of the vesicles, releasing their
hormones into the bloodstream.
 Hormones released by Posterior Pituitary gland

• Oxytocin and antidiuretic hormone (ADH, vasopressin) are the hormones

released from axon terminals within the posterior pituitary
•Oxytocin
•initiates labor
•stimulates mammary glands to release milk
•stimulates uterine contractions in activities other than labor

•Vasopressin (ADH) – decreases urine output.

Negative feedback regulation of secretion of
antidiuretic hormone (ADH)
 Disorders related with pituitary gland

• Gigantism is a very rare condition that happens when a child or adolescent has
high levels of growth hormone in their body, which causes them to grow very
tall.
 Disorders related with pituitary gland

• Acromegaly is a rare condition where the body produces too

much growth hormone, causing body tissues and bones to grow
more quickly
 Diabetes insipidus

• It happens when body doesn't have enough antidiuretic

hormone (ADH, or vasopressin)
 Thyroid gland
• The thyroid gland is situated in the neck in front of the larynx and trachea at the level
of the 5th, 6th and 7th cervical and 1st thoracic vertebrae.
• It is a highly vascular gland that weighs about 25 g and is surrounded by a fibrous
capsule.
• It resembles a butterfly in shape, consisting of two lobes
• One on either side of the thyroid cartilage and upper cartilaginous rings of the
trachea
 Thyroid Gland
• Location:
– Located in the anterior neck, in front of trachea
• Shape ,Size & weight:
– H or Butterfly shaped,Consisting of two lateral lobes connected by a
median tissue mass called the isthmus
– The largest pure endocrine gland, 12-15mm in Height
– Weight 15-20g
• Histology
– Internally, the gland is composed of hollow, spherical follicles or Acini
(50-500µm in diameter)
– The follicle walls are formed by cuboidal or squamous epithelial cells
called follicle cells
 Thyroid Gland

• Lumen of the follicle stores colloid, consisting of thyroglobulin + iodine

• Thyroid hormone is derived from this iodinated thyroglobulin
• T4 (93%) and T3 (7%)
– When the gland is inactive, the colloid is abundant, the follicles are large,
and the cells lining them are flat.
– When the gland is active, the follicles are small, the cells are cuboid or
columnar
• The parafollicular cells (C-cells)
– Don’t reach the lumen
– Lie in the follicular epithelium and protrude into the soft connective tissue
• Produce calcitonin, an entirely different hormone.
Thyroid Gland
 Thyroid Hormone
• Thyroid hormone – the body’s major metabolic hormone
• Consists of two closely related iodine-containing compounds
– T4 – thyroxine; has two tyrosine molecules plus four bound iodine
atoms
– T3 – triiodothyronine; has two tyrosines with three bound iodine
atoms
 T3 and T4 Structures

T 4 or Thyroxine T 3 or Triiodothyronine
Calcitonin
• A peptide hormone produced by the parafollicular, or C, cells
• Lowers blood calcium levels
• Antagonist to parathyroid hormone (PTH)
• Functions
• Calcitonin targets the skeleton, where it:
– Inhibits osteoclast activity and release of calcium from the bone
matrix
– Stimulates calcium uptake and incorporation into the bone matrix
• Regulated by a humoral (calcium ion concentration in the blood) negative feedback
mechanism
– Released by Rising blood levels of Ca2+ and inhibited by reverse
• Paget’s disease
– Characterized by a significant increase in osteoclast activity
and, thus, a high rate of bone turnover and hypercalcemia
Adrenal (Suprarenal) Glands
• Adrenal glands – paired, pyramid-shaped organs at top of
the kidneys, weigh 4 g each.
• Structurally and functionally, they are two glands in one
– Adrenal medulla – nervous tissue that acts as part of the
Sympathetic NS (20% of gland)
– Adrenal cortex – bulk of glandular tissue derived from
embryonic mesoderm encapsulating medulla
Adrenal Cortex

• Synthesizes and releases steroid hormones

called corticosteroids
• More than 24 corticosteroids are synthesized
• Different corticosteroids are produced in each of
the three layers
– Zona glomerulosa – mineralocorticoids
(chiefly aldosterone)
– Zona fasciculata – glucocorticoids
(chiefly cortisol)
– Zona reticularis – gonadocorticoids
Adrenal Cortex
Mineralocorticoids

• Regulation of the electrolyte concentrations of

extracellular fluids particularly Na+ and K+
• Aldosterone (95 %) – most important mineralocorticoid
– Maintains Na+ balance by reducing excretion of sodium from
the body
– Stimulates reabsorption of Na+ by the kidneys
• Promotes the synthesis of proteins needed for reabsorption of Na+ i.e
Na+/K+ -ATPase
– Its effects last for 20 minutes
• Aldosterone secretion is stimulated by:
Glucocorticoids

• Glucocorticoid hormones include

– cortisol (hydrocortisone)
– cortisone, and
– corticosterone,
• Only cortisol is secreted in significant amounts in humans.
• As for all steroid hormones, the basic mechanism of glucocorticoid activity on target cells
is to modify gene activity
• Cortisol
• Help the body resist stress by:
– Keeping blood sugar levels relatively constant
– Maintaining blood volume and preventing water shift into tissue
• Cortisol provokes:
– Gluconeogenesis (formation of glucose from noncarbohydrates)
– Rises in blood glucose, fatty acids, and amino acids
Gonadocorticoids (Sex Hormones)
• Most gonadocorticoids secreted are androgens (male sex
hormones), and the most important one is testosterone
• Androgens contribute to:
– The onset of puberty
– The appearance of secondary sex characteristics
• Androgens can be converted into estrogens after
menopause
 Adrenal Medulla

• Made up of chromaffin cells that secrete epinephrine

and norepinephrine
• Secretion of these hormones causes:
– Blood glucose levels to rise
– Blood vessels to constrict
– The heart to beat faster
– Blood to be diverted to the brain, heart, and skeletal muscle
Adrenal Medulla

• Epinephrine is the more potent stimulator of the heart

and metabolic activities
• Norepinephrine is more influential on peripheral
vasoconstriction and blood pressure