You are viewing an organ of the respiratory system and note the following tissues: folded mucosal layer containing simple cuboidal epithelium and smooth muscle, shifting into simple squamous epithelia. Identify the organ.

Respiratory bronchiole  

Explanation:

The respiratory bronchioles represent the narrowest airways within the lung, being continuations of terminal bronchioles that have approx. 0.5 mm in size. The epithelium of the respiratory bronchiole is composed of cuboidal ciliated cells and a small number of non-ciliated (secretory) Clara cells. The respiratory bronchioles lead into alveolar ducts composed of smooth muscle and connective tissue (i.e., elastin and collagen), connecting the respiratory bronchioles to the alveolar sacs.

d

explanation:

an individual’s sex (i.e., whether they are a male or female) is determined by the sex chromosomes. most people have two sex chromosomes, one that is inherited from their mother and one that is inherited from their father. typically, females have two x chromosomes (xx) and males have one x chromosome and one y chromosome (xy). conditions caused by changes (“mutations”) in genes located on the x chromosome are considered x-linked.

x-linked recessive inheritance

most x-linked conditions are recessive. this means that in a person with two x chromosomes (most females), both copies of a gene (i.e., one on each x chromosome) must have a change or mutation whereas in a person with one x chromosome (most males), only one copy of a gene must have a mutation. a female with a mutation in one copy of a gene on the x chromosome is said to be a “carrier” for an x-linked condition. a male with a mutation in a gene on the x chromosome is typically affected with the condition. because females have two copies of the x chromosome and males have only one x chromosome, x-linked recessive diseases are more common among males than females. however, x-linked recessive diseases can occur in both males and females.

for x-linked recessive disorders, an unaffected carrier mother who has a mutation in a gene on the x chromosome can transmit either the x chromosome with this mutation or a “normal” x chromosome to her children. if the father is unaffected, none of her daughters will be affected and all of her daughters will be unaffected—since they will inherit at least one normal x chromosome from their father. however, each daughter will have a 50% chance of being an unaffected carrier like her mother and a 50% chance of both x chromosomes being normal.