The hypothalamus and pituitary

Organ system: Endocrine system

Medical specialty: Endocrinology

This structure is a component of the brain. 

 

Anatomy

The hypothalamus is a structure of the brain. It sits below the thalamus (this is what hypo-thalamus means), but above the pituitary. 

The pituitary (also called the hypophysis) sits in the "sella turcica" in the floor of the sphenoid bone (one of the bones which comprise the skull).

 

Embryology

In early development, the prosencephalon (forebrain) divides into the diencephalon and telencephalon.

The telencephalon eventually becomes the cerebral cortex and the basal ganglia.
The diencephalon becomes the third ventricle, the thalamus, the hypothalamus and the posterior pituitary.

 

Physiology

The anterior pituitary is a gland which stores and releases important hormones into the circulatory system. The hypothalamus communicates with it through a rich system of blood vessels. This system is called the hypothalamic-hypophyseal portal system. 

The posterior pituitary is a collection of axonal projections (the transmitting fibres of neurons) from the hypothalamus. Hormones are secreted from these projections, into a network of blood vessels. 

The hypothalamus and the pituitary work as the bridge between the central nervous system and the endocrine system. By releasing hormones into the circulatory system, the brain can coordinate widespread cellular signalling throughout the whole body. These endocrine signals are slow to cause action, but the effects can last for a long time.
The spinal cord on the other hand, is useful for rapid signal transmission from the brain to the body.

 

Primary signalling targets

• Somatotropes
• Output: Human growth hormone (hGH)
• Effect: Stimulates growth in body cells
• Lactotropes
  • Output: Prolactin (PRL)
  • Effect: Stimulates milk production in the mammary glands
• Gonadotropes
• Output: Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH)
• Effect: Stimulates hormone release from the gonads
• Corticotropes 
• Output: Adrenocorticotropic hormone (ACTH)
• Effect: Stimulates hormone release from the adrenal glands
• Thryotropes
• Output: Thyroid stimulating hormone (TSH)
• Effect: Stimulates hormone release from the thyroid gland

• Posterior pituitary 
• Output: Oxytocin
• Effect: Stimulates milk ejection from the mammary glands 
• Effect: Stimulates muscular contractions of the uterus
• Posterior pituitary
• Output: Anti-diuretic hormone (Vasopressin)
• Effect: Promotes water retention in the kidneys

 

Hormones

• Human growth hormone (hGH)
• Prolactin (PRL)
• Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH)
• Adrenocorticotropic hormone (ACTH)
• Thyroid stimulating hormone (TSH)
• Oxytocin
• Anti-diuretic hormone (Vasopressin)

 

Pathology

• Hyperpituitarism (excessive pituitary activity) 
• Gigantism or acromegaly  
• Unexpected lactation
• Hypercortisolism (Cushing's disease)
• Hypopituitarism (insufficient pituitary activity)
• Oligo- or amenorrhoea  
• Infertility
• Pituitary dwarfism
• Hypocortisolism (Addison's disease) 
• Pituitary adenoma