Human Embryology and Endocrine System Fundamentals

Embryonic Development and Labor Stages

• Acrosome: The tip of the sperm’s head that releases enzymes that digest egg caps.
• Cleavage: A series of cell divisions without cell growth during the first four days after fertilization.
• Morphogenesis: The process of physical change where an organism becomes several different types of cells.
• Chorion: The outermost membrane.
• Neural groove: Becomes the brain and spinal cord.
• Pharyngeal arches: Become part of the face, neck, and mouth.
• Dilation stage: The first stage of labor is the longest and involves three phases: the Early Labor Phase is the time from the onset of labor until the cervix is dilated to 3 cm.

Hormones and Their Source Organs

Match the hormone with the organ that makes it and/or its effect on the body. Only major hormones of the anterior pituitary, pineal, thyroid, parathyroid, pancreas, and adrenal will be asked.

• Anterior pituitary: Produces hormones such as thyroid hormone.
• Pineal: Believed to coordinate the hormones of fertility in humans.
• Parathyroid: Secretes parathyroid hormone; increases blood calcium levels, stimulates osteoclasts to remove calcium from bone, and stimulates the kidneys and intestine to absorb more calcium.
• Pancreas: Produces insulin and glucagon.
• Adrenal: Responsible for the release of norepinephrine and epinephrine.

Major Endocrine Organs

Be able to identify our major endocrine organs found in our body: pituitary, thymus, thyroid, parathyroid, adrenal, pineal, ovary, testes, and pancreas.

Chemical Classes of Hormones

What chemical class do most hormones belong to? Which class is made from cholesterol?

Most hormones belong to the protein class. The class made from cholesterol belongs to steroids.

Hormone Binding and Target Cells

What do the target cells have that allow certain hormones to bind to them? Can any hormone act on any cell?

Hormones affect only certain tissues or organs (target cells or target organs). Target cells must have specific protein receptors. Hormone binding alters cellular activity; therefore, not every hormone can act on every cell.

Negative Feedback Mechanisms

What is negative feedback? How are hormones involved in this?

Hormone levels in the blood are maintained mostly by negative feedback. This is a reaction that causes a decrease in function in response to some kind of stimulus. Often, it causes the output of a system to be lessened.

Categories of Endocrine Gland Stimuli

The stimuli that activate endocrine glands fall into three major categories:

1. Hormonal: Endocrine organs are activated by other hormones (e.g., produces hormones that stimulate the anterior portion of the pituitary gland).
2. Humoral: Changing blood levels of certain ions and nutrients stimulate hormone release (e.g., a rise in blood glucose).
3. Neural: Nerve impulses stimulate hormone release (e.g., the release of adrenaline).

Pure vs. Mixed Endocrine Glands

Are the pancreas, testes, and ovaries examples of a purely endocrine gland or mixed? Why?

No. Some glands are purely endocrine, such as the anterior pituitary, thyroid, adrenals, and parathyroids. Endocrine glands are ductless glands where hormones are released directly into the blood or lymph. The pancreas, testes, and ovaries are considered mixed glands.

Stress and the Fight-or-Flight Response

Which endocrine gland produces hormones that deal with stress and is our “fight or flight” response?

The adrenal medulla and adrenal cortex.