Relationship Between Hypothalamus and Pituitary Gland

Hypothalamus and pituitary gland are primary endocrine glands of the human body. Hypothalamus is a small area of the brain, which is located under the thalamus. The pituitary gland is located just below the hypothalamus. The pituitary gland comprises two lobes; anterior lobe (adenohypophysis) and posterior lobe (neurohypophysis). The hypothalamus is connected to the anterior lobe of the pituitary gland by means of a special portal blood system. Moreover, the hypothalamus is directly connected to the posterior lobe of the pituitary gland by means of neurons. Therefore, the hypothalamus regulates the function of the pituitary gland. This is the relationship between hypothalamus and pituitary gland.

Key Areas Covered

1. What is Hypothalamus
      – Definition, Anatomy, Physiology and Function
2. What is Pituitary Gland
      – Definition, Anatomy, Physiology and Function
3. Relationship Between Hypothalamus and Pituitary Gland
      – Vascular and Neuronal Connection
      – Similarities

Key Terms: Anterior Pituitary Gland, Autonomic Nervous System, Brain, Infundibulum, Homeostasis, Hypophyseal Portal Veins, Hypothalamus, Neurosecretory Cells, Posterior Pituitary Gland

What is Hypothalamus

Hypothalamus is a region of the forebrain below the thalamus, which coordinates both autonomic nervous system and the functioning of the pituitary gland. It is connected to the two lobes of the pituitary gland via vascular and neuronal pathways. The hypothalamus is shown in figure 1.

Figure 1: Hypothalamus

The main function of the hypothalamus is to maintain the homeostasis of the body. It responds to a variety of internal and external signals of the body via the nervous system. It controls the blood pressure, the levels of circulating hormones, body temperature, hunger, thirst, sleep, and emotional activity. The function of the autonomic nervous system is also controlled by the hypothalamus. Two types of hormones are produced by the hypothalamus. One type of hormones are sent to the posterior pituitary gland for the secretion. They are the antidiuretic hormone and oxytocin. Antidiuretic hormone reabsorbs water from the kidney. Oxytocin contracts the uterus during the childbirth and releases breast milk. The other type of hormones may contain inhibitory or stimulating actions on the secondary endocrine organs of the body. These hormones are sent to the anterior pituitary gland for the secretion. Dopamine, somatostatin, corticotrophin-releasing hormone (CRH), growth hormone-releasing hormone (GHRH), thyrotrophin-releasing hormone (TRH), and gonadotrophin-releasing hormone (GnRH) are some of the hormones released by the hypothalamus.

What is Pituitary Gland

The pituitary gland is the major endocrine gland, which is attached to the base of the brain and controls the production and release of hormones from other endocrine glands. It is a pea-sized organ, accounting for less than 1% of the total weight of the brain. The two lobes of the pituitary gland are called the anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis). The anterior pituitary comprises glandular cells. The posterior pituitary gland comprises nerve cells. The structure of the pituitary gland is shown in figure 2.

Figure 2: Pituitary Gland

Human growth hormone (hGH), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), prolactin (PRL), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and melanocyte-stimulating hormone (MSH) are the seven hormones produced by the anterior pituitary gland. Posterior pituitary secretes the hormones produced in the hypothalamus.

The secretions of the other endocrine glands are regulated by the hormones secreted by the pituitary gland. Therefore, the pituitary gland is called the master gland of the body. It regulates the secretion of hormones from the adrenal gland, thyroid gland, hypothalamus, thymus, pineal gland, pancreas, and gonads. Through these hormones, growth, development, metabolism, blood pressure, sexual maturation, and reproduction are controlled.

Relationship Between Hypothalamus and Pituitary Gland

Vascular Connection

Hypothalamus is located below the thalamus whereas pituitary gland is located below the hypothalamus. The pituitary gland is attached to the hypothalamus by a stalk. Hypothalamus is connected to the both lobes of the pituitary gland. It connects to the anterior pituitary gland by means of a portal blood system. Therefore, the communication between hypothalamus and anterior pituitary gland occurs via chemical signals (stimulating and inhibiting hormones). Those chemical signals are produced by the neurosecretory cells in the hypothalamus. They are released to a capillary network called primary plexus in order to be transported through the hypophyseal portal veins to a second capillary network called secondary plexus. The primary plexus, as well as the hypophyseal portal veins, belong to the infundibulum. The secondary plexus belongs to the anterior pituitary. The anterior pituitary complex is shown in figure 3.

Figure 3: Anterior Pituitary Complex

Neuronal Connection

Some neurosecretory cells expand a short distance from the hypothalamus to the posterior pituitary through the infundibulum. The hormones produced by those neurosecretory cells are stored in vesicles and transported through the axons. The storage of those hormones occurs at the axon terminals at the posterior pituitary. When the neurosecretory cells are stimulated, the hormones in the vesicles are released to the capillary network in the posterior pituitary. The posterior pituitary complex is shown in figure 4.

Figure 4: Posterior Pituitary Complex

Due to the connection between the hypothalamus and the two lobes of the pituitary gland, the pituitary gland is involved in the storage and the release of hormones produced by the hypothalamus into the bloodstream.

Similarities Between Hypothalamus and Pituitary Gland

• Both hypothalamus and pituitary gland are primary endocrine glands, which produce and secrete hormones.
• Both hypothalamus and pituitary gland are located in the brain below the thalamus.

Conclusion

Hypothalamus and pituitary gland are two endocrine glands that control the production and release of hormones of the other endocrine glands in the body. Both hypothalamus and pituitary gland are located in the brain, very close to each other. Hypothalamus is connected to the anterior and the posterior lobes of the pituitary gland. Hypothalamus maintains the homeostasis of the body and pituitary gland controls growth, development, and the metabolism of the body. 

Reference:

1. “Hypothalamus.” You and Your Hormones, Available here. Accessed 3 Oct. 2017.
2. “Pituitary Gland.” InnerBody, Available here. Accessed 3 Oct. 2017.
3. StephenBrowne. “The Connection between the Pituitary and Hypothalamus?” Thyroid, Parathyroid, Adrenal, Endocrine Surgery, The Connection between the Pituitary and Hypothalamus?, Available here. Accessed 3 Oct. 2017.

Image Courtesy:

1. “Figure 35 03 06” By CNX OpenStax – (CC BY 4.0) via Commons Wikimedia
2. “Gray1181” By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body, Bartleby.com: Gray’s Anatomy, Plate 1181 (Public Domain) via Commons Wikimedia
3. “1808 The Anterior Pituitary Complex” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia
4. “1807 The Posterior Pituitary Complex” By OpenStax College – Anatomy & Physiology, Connexions Web site. Available here, Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia