What are the two branches of the somatic nervous system?

Spinal nerves and Cranial nerves

Spinal nerves: They are mixed nerves that carry sensory information into and motor commands out of the spinal cord.

Cranial nerves: They are the nerve fibers that carry information into and out of the brain stem.

the corpus luteum secretes estrogens and progesterone. the latter hormone causes changes in the uterus that make it more suitable for implantation of the fertilized ovum and the nourishment of the embryo. if the egg is not fertilized, the corpus luteum becomes inactive after 10–14 days, and menstruation occurs.

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enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products